Planographic printing plate and method of producing the same

ABSTRACT

A negative planographic printing plate comprising a substrate carrying thereon a recording layer which contains a polymerizable compound and an infrared absorbing agent, and in which a polymerization reaction caused the action of light or heat decreases solubility in an alkali developer, wherein the optical density of said recording layer is from 0.4 to 2.0, and the film hardness of the upper part of said recording layer after reduction in solubility in an alkali developer due to the action of light or heat is higher than the average film hardness of the whole recording layer, and a preferable method of producing the same.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a planographic printing platehaving sensitivity in an infrared wavelength region and a method ofproducing the same. More particularly, the present invention relates toa negative planographic printing plate which can be obtained byso-called direct plate production in which plate production can bedirectly effected by using infrared laser based on digital signals fromcomputers and the like.

[0003] 2. Description of the Related Art

[0004] Recently, there are remarkable developments in lasers.Particularly, solid laser and semiconductor laser which emit an infraredray having a wavelength from 760 nm to 1200 nm (hereinafter, sometimesreferred to as “infrared laser”), and show high output and have smallsize are easily available. These infrared lasers are very useful as arecording light source in directly producing a printing plate platesbased on digital data from computers and the like. Therefore, there is,recently, increasing desire for an image recording material having highsensitivity, for such an infrared recording light source, namely, animage recording material whose solubility in a developer changessignificantly due to irradiation with an infrared ray.

[0005] As such a negative image recording material which can be recordedby infrared laser, U.S. Pat. No. 5,340,699 describes a recordingmaterial composed of an infrared absorbing agent, an acid generator,resol resin and a novolak resin. However, such a negative imagerecording material requires, for image formation, a heating treatmentafter exposure with the laser. Therefore, a negative image recordingmaterial requiring no heating treatment after exposure has been desired.

[0006] Further, in a method using exposure of high power and intensityand utilizing a high output laser, an exposure region is irradiatedintensively with a large amount of light energy for an exposure time ofan instant. This light energy is converted efficiently into heat energyand thermal changes such as chemical changes, phase changes and, changesin form and structure are caused by this heat, and the changes areutilized for image recording. However, when the amount of an infraredabsorbing agent added is increased for improvement of recordingsensitivity in a recording layer of a conventional planographic printingplate, a laser exposure apparatus and a light source may becomecontaminated due to ablation (splashing) of the recording layer.

[0007] For achieving the two objects of improvement of image formationproperty and suppression of ablation, JP-A No. 11-192782 describes animage formation material having a structure containing two laminatedrecording layers having different functions respectively, however, thismaterial is of positive type, and different from the present invention.

[0008] As a negative image formation material, WO 97/00777, for example,describes a negative image formation material having a photosensitivelayer with a two-layer structure. However, there is a problem with thisstructure in that ablation tends to occur since the surface layer whichis an exposure surface is photosensitive, and further, post-exposure isnecessary for obtaining a strong image.

[0009] One object of the present invention is to provide a negativeplanographic printing plate which can manifest direct plate productionby recording based on digital data from a computer and the like usingsolid laser and semiconductor laser emitting infrared rays, shows highsensitivity to infrared laser, suppresses ablation of a recording layerin recording, and has excellent image formation properties such as dotreproduction property and excellent printing endurance, and anotherobject is to provide a preferable method of producing the same.

SUMMARY OF THE INVENTION

[0010] The present inventors have directed their attention to theproperty of a recording layer of a negative planographic printing platewhich can realize direct plate production by irradiation with infraredray and intensively studied this. As a result, they have found that theabove-mentioned problems can be solved by causing the film hardness nearthe surface of a recording layer which is hardened by exposure with alaser to be higher than the film hardness of the entire body. Further,they found a plate production method for developing a planographicprinting plate having such a recording layer using a developer havingspecific properties. These discoveries led to completion of the presentinvention.

[0011] Namely, the planographic printing plate of the present inventionis a planographic printing plate comprising a substrate carrying thereona recording layer which contains a polymerizable compound and aninfrared absorbing agent, and causes a polymerization reaction by theaction of light or heat to decrease solubility in an alkali developer,wherein the optical density of the recording layer is from 0.4 to 2.0,and the film hardness of the upper part of the recording layer afterreduction in solubility in an alkali developer due to the action oflight or heat is higher than the average film hardness of the recordinglayer.

[0012] In a preferable embodiment, the above-mentioned recording layercontains an infrared absorbing agent under conditions causing noablation.

[0013] Further, in a certain embodiment, the method of producing aplanographic printing plate of the present invention comprises exposinga planographic printing plate containing a substrate carrying thereon arecording layer which contains a polymerizable compound and an infraredabsorbing agent, and causes a polymerization reaction by the action oflight or heat to decrease solubility in an alkali developer, wherein theoptical density of the recording layer is from 0.4 to 2.0, and the filmhardness of the upper part of the recording layer after reduction insolubility in an alkali developer due to the action of light or heat ishigher than the average film hardness of the recording layer, then,developing the plate by a developer showing lower permeability throughthe recording layer after hardening.

[0014] In the present invention, the expression “by the action of lightor heat” also means “by both of the action of light and the action ofheat”.

[0015] Though the action of the present invention is not explicit, it isspeculated that at the exposed surface of a recording layer whosesolubility in an alkali developer decreases by exposure at or near theexposed surface, sensitivity to infrared laser is excellent, filmhardness due to a polymerization reaction is high, and in the deeperportions of a recording layer, film hardness becomes lower because ofdiffusion of heat to a substrate. However, when such a photosensitivelayer is developed after hardening (polymerization reaction), portionsaround the surface of a recording layer manifest lower permeability toan alkali developer and function as a protective layer. Consequently,development stability becomes excellent and an image having excellentdiscrimination is formed, and simultaneously, stability long-term isalso obtained.

[0016] Further, it is believed that, in production of a planographicprinting plate having such a recording layer, by selecting a developercapable of optimum permeation through a recording layer based onelectrostatic capacity described later and by effecting development withsuch a developer, the developer does not easily permeate portion in thevicinity of a substrate which have relatively lower hardness and botheffects of increase in sensitivity and prevention of decrease inprinting endurance can be satisfactorily achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 is a schematic structual view showing one example of amethod of measuring electrostatic capacity used for evaluation ofpermeability of a developer into a photosensitive layer.

[0018]FIG. 2 is a graph showing a relation between an immersion time ofa planographic printing plate into a typical developer (voltageapplication time) and electrostatic capacity of the developer.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The present invention will be described in detail below.

[0020] The planographic printing plate of the present inventioncomprises a recording layer having a polymerizable compound and aninfrared absorbing agent, and in which a polymerization reaction iscaused by the action of light or heat to thereby decrease solubility ofthe recording layer in an alkali developer, and in which, the opticaldensity of the recording layer is from 0.4 to 2.0, and the film hardnessof the upper portion of the recording layer after reduction insolubility in an alkali developer owing to hardening of the recordinglayer due to the action of light or heat is higher than the average filmhardness of the recording layer.

[0021] In the planographic printing plate of the present invention, itis satisfactory that a recording layer as described above is provided ona substrate, and further, known layers such as a surface layer,intermediate layer, back coat layer and-the like may also be provided aslong as the effect of the present invention is not impaired.

[0022] Recording Layer

[0023] A recording layer of the planographic printing plate of thepresent invention is preferably formed on the exposure surface of thetop layer of the planographic printing plate, and an infrared absorbingagent generates heat due to exposure to an infrared laser, apolymerization reaction occurs due to this heat, and only exposedportions of the recording layer are hardened to manifest lowering insolubility in an alkali developer.

[0024] An example of such typical recording layers is aphotopolymerizable layer. The photopolymerizable layer contains (A) aninfrared absorbing agent, (B) a radical generator and (C) aradical-polymerizable compound which causes a polymerization reactionwith the generated radical and thereby causes hardening, and preferably,further contains (D) a binder polymer. The infrared absorbing agentconverts absorbed infrared ray into heat, and a radical polymerizationinitiator such as an onium salt and the like is decomposed by heatgenerated in this conversion, to generate a radical. Theradical-polymerizable compound is selected from compounds having atleast one ethylenically unsaturated double bond, and at least one,andpreferably two or more terminal ethylenically unsaturated bonds, and thegenerated radical causes chain polymerization reactions, and results inhardening.

[0025] The optical density of the recording layer of the presentinvention, specifically, the reflection density caused by an infraredabsorbing agent in a recording layer for the exposed wavelength is from0.4 to 2.0, and preferably from 0.6 to 1.6, and an infrared absorbed isso contained that the optical density is relatively high. Therefore, dueto exposure using infra-red rays, a polymerization reaction isgenerated, and this reaction proceeds quickly in the vicinity of thesurface of the recording layer, and thus high film hardness is achived.However, an infrared laser used for exposure does not easily permeateinto the deeper portion of the recording layer, and further, heat isdiffused to a substrate, and the film hardness around a substrate islower in comparison. The film hardness of the upper portion of therecording layer is thus higher than the average film hardness of therecording layer. Here, the upper portion of the recording layer refer toa portion within 20% of the thickness of the recording layer from thesurface there of.

[0026] For the difference between the film hardness of the upper portionof a recording layer after hardening and the average film hardness, theratio of the film hardness of the upper portion of a recording layer tothe average film hardness [value of (upper portion film hardness/averagefilm hardness)] is preferably 1.2 or more, and further preferably from20 to 1.3. When this difference is small and the above-mentioned valueis too near 1, the discrimination of an image formed tends to decrease.Further, where the difference is extremely large there maybe, reductionin close adherence at the interface with a substrate. That is, neitherof the above cases is desirable.

[0027] The film hardness can be measured by an ordinary method, andspecifically, for example, an ultra micro extrusion hardness measuringapparatus formd by combining of a microscope equipped with apiezo-actuator, with a transducer is used, and an indenter having atriangle pyramidal tip is extruded into a recording layer, anddisplacement and load are measured to give a displacement curve, and thefilm hardness is read from this curve.

[0028] Here, the film hardness (H) is represented by L_(max)/A whereinL_(max) means the maximum load and A means the contact sectional area ofan indenter in recording the maximum load. The contact sectional area Acan be calculated from gradient h_(plastic) of a tangential line drawnby linear approximation of the initial 30% of a gradual loading curvebased on the aspect ratio of the indenter. The film hardnesses of theupper part of a recording layer and the whole layer are measuredaccording to this method of measuring film hardness, by controlling thedepth (h_(total)) to which the indenter is thrusted.

[0029] Specifically, a method described in X. Yun, R. Hsiao, D. B. Bogy,C. S. Bhatia, ComputerMechanics Laboratory, Technical Report No. 96-015,1 (1996) can be applied, and in the present invention, Triboscope (tradename), a thrusting apparatus manufactured by HYSITRON is used as ameasuring apparatus, and is installed on AFM (interatomic forcemicroscope) SPA 300 (trade name, manufactured by Seiko InstrumentsK.K.), and the measured value is used.

[0030] Compounds used in a recording layer of a negative planographicprinting plate will be described below.

[0031] (A) Infrared Absorbing Agent

[0032] A recording layer of the planographic printing plate of thepresent invention has a composion which can effect image recording by alaser which emits infrared rays. In such a recording layer, an infraredabsorbing agent is preferably used. The infrared absorbing agentfunctions to convert absorbed infrared ray into heat. By heat generatedin this reaction, a radical generator and an acid generator aredecomposed to generate a radical and an acid. The infrared ray absorberused in the present invention is a dye or pigment showing an absorptionmaximum in the range from 760 nm to 1200 nm.

[0033] As the dye, commercially available dyes and, known materialsdescribed in literatures such as, for example, “Dye Manual” (edited byYuki Gosei Kagaku Kyokai, 1960) and the like can be used. Specifically,examples include those described in paragraph numbers [0050] to [0051]of JP-A No. 10-39509.

[0034] Of these dyes, cyanine colorants, squarylium colorants, pyryliumsalts, nickel thiolate complex are listed as particularly preferableexamples. Further, cyanine colorants are preferable, and cyaninecolorants of the following general formula (I) are most preferable.

[0035] In the general formula (I), X1 represents a halogen atom or X²—L¹or NL²N³. Here, X2 represents an oxygen atom or sulfur atom, and L¹represents a hydrocarbon group having 1 to 12 carbon atoms. Each of L²and L³ independently represents a hydrocarbon group having 1 to 12carbon atoms. Each of R¹ and R² independently represents a hydrocarbongroup having 1 to 12 carbon atoms. From the standpoint of storagestability of a photosensitive layer application solution, R¹ and R² arepreferably a hydrocarbon group having 2 or more carbon atoms, andfurther, it is particularly preferable that R¹ and R² are connected toeach other to form a 5-membered or 6-membered ring.

[0036] Ar¹ and Ar² may be the same or different, and represent anaromatic hydrocarbon group which may have a substituent. Y¹ and Y² maybe the same or different, and represent a dialkylmethylene group having12 or less sulfur atoms or carbon atoms. R³ and R⁴ may be the same ordifferent, and represent a hydrocarbon group having 20 or less carbonatoms and which may have a substituent. Examples of the preferablesubstituent are alkoxy groups having 12 or less carbon atoms, carboxylgroups and sulfo groups. R⁵, R⁶, R⁷ and R⁸ may be the same or different,and represent a hydrogen atom or a hydrocarbon group having 12 or lesscarbon atoms. From the standpoint of availability, they preferablyrepresent a hydrogen atom. Z¹⁻ represents a counter anion. However, whenany of R¹ to R⁸ is substituted with a sulfo group, Z¹⁻ is not necessary.As Z¹⁻, preferable are halogen ions, perchlorate ion, tetrafluoroborateion, hexafluorophosphate ion and sulfonate ion, and particularlypreferable are a perchlorate ion, hexafluorophosphate ion andarylsulfonate ion, from the standpoint of storage stability of aphotosensitive layer application solution.

[0037] As the specific examples of cyanine colorants of the generalformula (I) which can be suitably used in the present invention, thosedescribed in Japanese Patent Application No. 11-310623, paragraph nos.[0017] to [0019] are listed.

[0038] As the pigment used in the present invention, commerciallyavailable pigments, and pigments described in Color Index (C. I.)manual, “Saishin Ganryo Binran (Current Pigment Manual)” (edited byNippon Ganryo Gijutsu Kyokai, 1977), “Saishin Ganryo Oyo Gijutsu(Current Pigment Application Technology)” (published by CMC, 1986),“Insatsu Inki Gijutsu (Printing Ink Technology)” (published by CMC,1984) can be utilized.

[0039] Examples of the pigments include black pigments, yellow pigments,orange pigments, brown pigments, red pigments, violet pigments, bluepigments, green pigments, fluorescent pigments, metal powder pigments,and additionally, polymer bond pigments. Details of these pigments aredescribed in paragraph numbers [0052] to [0054] of JP-A No. 10-39509,and these can also be applied in the present invention. Of thesepigments, preferable is carbon black.

[0040] It is preferable that the content of the above-mentioned dye orpigment in a recording layer is so selected that ablation does not occurin the recording layer and the optical density for wavelengths ofinfrared laser is from 0.4 to 2.0.

[0041] Namely, when the amount of an infrared absorbing agent in arecording layer is too large, sudden increased heat generation occurslocally at portions exposed to infrared laser, and possibility ofablation of the whole recording layer increases. Further, the filmhardness at deeper portion of a recording layer becomes too low and apossibility of reduction in printing endurance occurs. On the otherhand, when the optical density is too low, the infrared laser used forwriting reaches deeper portions of the recording layer, leading to adifficulty changing film hardness along the thickness direction of arecording layer.

[0042] From the standpoint of ablation only, even if the optical densityof a recording layer is over 2.0, when the heat capacity of the wholerecording layer is large, heat is diffused in the layer, and ablationdoes not occur. Therefore, the amount of an infrared absorbing agentshould not necessarily be determined only by optical density. Indetermining the content of an infrared absorbing agent for improvementof sensitivity, it is preferable that the content thereof isappropriately determined in view of other components in the recordinglayer or the thickness of the layer while considering optical density.

[0043] (B) A Compound which Generates a Radical

[0044] As the compound generating a radical which is suitably used inthe present invention, onium salts, and specifically, iodonium salts,diazonium salts and sulfonium salts are preferably used. Though theseonium salts also function as an acid generator, when the onium salts areused together with a radical polymerizable compound described later,they function as an initiator for radical polymerization. The oniumsalts suitably used in the present invention are onium salts of thefollowing general formulae (III) to (V).

Ar¹¹—I⁺Ar¹² Z¹¹⁻  General formula (III)

Ar²¹—N⁺≡N Z²¹⁻  General formula (IV)

[0045]

[0046] In the formula (III), each of Ar¹¹ and Ar¹² independentlyrepresents an aryl group having 20 or less carbon atoms and which mayhave having a substituent. When this aryl group has a substituent,preferable examples of the substituent include halogen atoms, nitrogroup, alkyl groups having 12 or less carbon atoms, alkoxy groups having12 or less carbon atoms, or aryloxy groups having 12 or less carbonatoms. Z¹¹⁻ represents a counter ion selected from the group consistingof halogen ions, perchlorate ion, carboxylate ion, tetrafluoroborateion, hexafluorophosphate ion, and sulfonate ion, and preferable are aperchlorate ion, hexafluorophosphate ion and arylsulfonate ion.

[0047] In the formula (IV), Ar²¹ represents an aryl group having 20 orless carbon atoms and which may have a substituent. Examples of thepreferable substituent include halogen atoms, nitro group, alkyl groupshaving 12 or less carbon atoms, alkoxy groups having 12 or less carbonatoms, aryloxy groups having 12 or less carbon atoms, alkylamino groupshaving 12 or less carbon atoms, dialkylamino groups having 12 or lesscarbon atoms, arylamino groups having 12 or less carbon atoms anddiarylamino groups having 12 or less carbon atoms. Z²¹⁻ represents acounter ion as defined for Z¹¹⁻.

[0048] In the general formula (V), R³¹, R³² and R³³ may be the same ordifferent, and represent a hydrocarbon group having 20 or less carbonatoms and which may have a substituent. Examples of preferablesubstituents include halogen atoms, nitro group, alkyl groups having 12or less carbon atoms, aryloxy groups having 12 or less carbon atoms.Z³¹⁻ represents a counter ion as defined for Z¹¹⁻.

[0049] Specific examples of onium salts which can be suitably used inthe present invention, include those described in Japanese PatentApplication No. 11-310623, paragraph nos. [0030] to [0033], and JapanesePatent Application No. 2000-160323, paragraph nos. [0015] to [0046],filed previously by the present applicant.

[0050] The onium salt used in the present invention has a maximumabsorption wavelength preferably of 400 nm or less, and furtherpreferably of 360 nm or less. By thus controlling the absorptionwavelength within the ultraviolet region, a planographic printing platecan be handled under white light.

[0051] These onium salts can be added into a photosensitive layerapplication solution in a proportion of from 0.1 to 50% by weight,preferably from 0.5 to 30% by weight, and particularly preferably from 1to 20% by weight based on the total weight of all solid components inthe photosensitive layer application solution. When the addition amountis less than 0.1% by weight, sensitivity lowers, and when over 50% byweight, staining occurs on non-image portions in printing. These oniumsalts may be used alone or in combination of two or more. Further, theseonium salts may be added, together with other components, to the samelayer, or another layer may be provided to which the onium salts areadded.

[0052] (C) Radical Polymerizable Compound

[0053] The radical polymerizable compound used in a recording layer inthe present invention is a radical polymerizable compound having atleast one ethylenically unsaturated double bond, and is selected fromcompounds having at least one, and preferably two or more terminalethylenically unsaturated bonds. Such a compound group is widely knownin the art, and in the present invention, these compounds can be usedwithout specific restriction. They have a chemical form, such as, forexample, a monomer, prepolymer, namely, dimer, trimer and oligomer, or amixture thereof and a copolymer thereof, or the like. Examples of amonomer and copolymer thereof, include unsaturated carboxylic acids(e.g., acrylic acid, methacrylic acid, itaconic acid, crotonic acid,isocrotonic acid, maleic acid and the like) , esters thereof, andamides, and preferably, esters of an unsaturated carboxylic acid with analiphatic polyhydric alcohol compound, or amides of an unsaturatedcarboxylic acid with an aliphatic polyvalent amine compound, are used.Further, unsaturated carboxylates having a nucleophilic substituent suchas a hydroxyl group, amino group, mercapto group and the like, adductsof amides with monofunctional or polyfunctional isocyanates, or epoxys,dehydration condensation reaction products with a monofunctional orpolyfunctional carboxylic acid, and the like are suitably used. Further,adducts of an unsaturated carboxylate having an electrophilicsubstituent such as an isocyanate group, epoxy group and the like, oramides with monofunctional or polyfunctional alcohols, amines andthiols, and, substitution reaction products of an unsaturatedcarboxylate having a releasable substituent such as a halogen group,tosyloxy group and the like, or amides with monofunctional orpolyfunctional alcohols, amines and thiols, are also suitable. As otherexamples, compounds obtained by substituting the above-mentionedunsaturated carboxylic acid by an unsaturated phosphonic acid, styreneand the like can also be used.

[0054] Specific examples of acrylates, methacrylates, itaconates,crotonates, isocrotonates and maleates which are a radical polymerizablecompound which is an ester of a aliphatic polyhydric alcohol compoundwith an unsaturated carboxylic acid are described in Japanese PatentApplication No. 11-310623, paragraph nos. [0037] to [0042], and thesecompounds can also be applied to the present invention.

[0055] As examples of other esters, for example, aliphatic alcohol-basedesters described in JP-B Nos. 46-27926, 51-47334 and 57-196231, estershaving an aromatic skeleton described in JP-A Nos. 59-5240, 59-5241 and2-226149, esters having an amino group described in JP-A No. 1-165613,and the like can also be suitably used.

[0056] As specific examples of a monomer of an amide of an aliphaticpolyvalent amine compound with an unsaturated carboxylic acid, there aremethylenebis-acrylamide, methylenebis-methacrylamide,1,6-hexamethylenebis-acrylamide, 1,6-hexamethylenebis-methacrylamide,diethylenetriaminetrisacrylamide, xylylenebisacrylamide,xylylenebismethacrylamide and the like.

[0057] Examples of other preferable amide-based monomers includemonomers having a cyclohexylene structure described in JP-B No.54-21726.

[0058] Further, urethane-based addition polymerizable compounds producedby using an addition reaction of an isocyanate with a hydroxyl group arealso suitable, and as specific examples thereof include vinylurethanecompounds containing two or more polymerizable vinyl groups in onemolecule obtained by adding a vinyl monomer having a hydroxyl group ofthe following general formula (VI) to a polyisocyanate compound havingtwo or more isocyanate groups in one molecule described in JP-B No.48-41708, and the like.

CH₂=C(R⁴¹)COOCH₂CH(R⁴²)OII  General formula (VI)

[0059] (wherein, R⁴¹ and R⁴² represent II or CH₃)

[0060] Also, urethane acrylates as described in JP-A No. 51-37193, JP-BNos. 2-32293 and 2-16765, and urethane compounds having an ethyleneoxide-based skeleton described in JP-B Nos. 58-49860, 56-17654, 62-39417and 62-39418 are suitable.

[0061] Further, radical polymerizable compounds having an aminostructure or sulfide structure in the molecule described in JP-A Nos.63-277653, 63-260909 and 1-105238 may also be used.

[0062] Other examples include polyfunctional acrylates andmethacrylates, such as polyester acrylates as described in JP-A Nos.48-64183 and 49-43191 and JP-B No. 52-30490, epoxy acrylates obtained byreacting an epoxy resin with a (meth)acrylic acid, and the like.Furthermore, specific unsaturated compounds described in JP-B Nos.46-43946, 1-40337 and 1-40336, and vinylphosphonic acid-based compoundsdescribed in JP-A No. 2-25493, and the like can also be used. In somecases, structures containing a perfluoroalkyl group described in JP-ANo. 61-22048 are suitably used. Further, those introduced asphotosetting monomers and oligomers in Nippon Secchaku Kyokai Shi(Japanese Adhesion Institution Journal) vol. 20, No. 7, pp. 300 to 308(1984) can also be used.

[0063] Details of the method of using these radical polymerizablecompounds such as the kind of a structure used, whether it is usedsingly or combined, the addition amount, and the like, can be optionallyset according to the desired function of the final recording material.Regarding sensitivity, a structure having high content of unsaturatedgroups per molecule is preferable. In many cases, two or more functionalstructure is preferable. For enhancing the strength of an image portion,namely, a hardened film, a structure having three or more functiongroupes is preferably used. Using combination of compounds havingdifferent numbers of functional groups and different polymerizablegroups (e.g., acrylate-based compound, methacrylate-based compound,styrene-based compound and the like) is also preferably used forcontrolling both of photosensitivity and strength.

[0064] The preferable compounding ratio of a radical polymerizablecompound is, in may cases, from 5 to 80% by weight, and preferably from20 to 75% by weight based on the total weight of all components in thecomposition. These may be used alone or in combination of two or more.In addition, regarding the use method of a radical polymerizablecompound, a suitable structure, compounding ratio and addition amountcan be optionally selected from the standpoints of the extent ofpolymerization inhibition on oxygen, resolution, fogging property,variation in refractive index, surface stickiness, and the like, andfurther, in some cases, layer structures and application methods such aspriming and finishing can also be effected.

[0065] (D) Binder Polymer

[0066] In the present invention, a binder polymer is also used. As thebinder, a linear organic polymer is preferably used. As such “linearorganic polymer”, any polymer may be used. Preferably, for enablingdevelopment with water or development with weak alkaline water, linearorganic polymers which are soluble in or swellable with water or weakalkaline water are selected. The linear organic polymer is selected foruse, based not only on use as a film forming agent for forming aphotosensitive layer, but based also on use with water, weak alkalinewater or organic solvent developer. For example, when a water-solubleorganic polymer is used, developing with water becomes possible. As sucha linear organic polymer, there are radical polymers having a carboxylgroup as the side chain, for example, those described in JP-A No.59-44615, JP-B Nos. 54-34327, 58-12577 and 54-25957, JP-A No. 54-92723,59-53836 and 59-71048, namely, methacrylic acid copolymers, acrylic acidcopolymers, itaconic acid copolymers, crotonic acid copolymers, maleicacid copolymers, partially esterified maleic acid copolymer, and thelike. Further, there are acidic cellulose derivatives having a carboxylgroup as the side chain likewise. In addition, those obtained by addinga cyclic acid anhydride to a polymer having a hydroxyl group, and thelike, are useful.

[0067] Particularly, among those compounds, (meth)acrylic resins havinga benzyl group or allyl group, and a carboxyl group as the side chainsare suitable since they are excellent in attaining balance between filmstrength, sensitivity and developing property.

[0068] Further, as the binder polymer, “water-insoluble and alkaliwater-soluble polymers” described below (hereinafter, appropriatelyreferred to simply as alkali water-soluble polymer) can also be used.

[0069] The alkali water-soluble polymer is a water-insoluble and alkaliwater-soluble polymer and has excellent film forming property,therefore, can form a layer.

[0070] The alkali water-soluble polymer in the present inventionincludes homo-polymers containing an acidic group on the main chainand/or side chain in a polymer and copolymers thereof or mixturesthereof. Therefore, a polymer layer in the present invention has such aproperty that, when contacted with an alkaline developer, it isdissolved in the developer.

[0071] Among them, those having an acidic group exemplified in thefollowing (1) to (6) on the main chain and/or side chain of the polymerare preferable from the standpoint of solubility in an alkalinedeveloping solution.

[0072] (1) Phenol group (—Ar—OH)

[0073] (2) Sulfoneamide group (—SO₂NH—R)

[0074] (3) Substituted sulfoneamide-based acid group (hereinafter,referred to as “active imide group”) [—SO₂NHCOR, —SO₂NHSO₂R, —CONHSO₂R]

[0075] (4) Carboxyl group (—CO₂H)

[0076] (5) Sulfonic group (—SO₃H)

[0077] (6) Phosphoric group (—OPO₃H₂)

[0078] In the above-mentioned (1) to (6), Ar represents a di-valent arylconnecting group which may have a substituent, and R represents ahydrocarbon group which may have a substituent.

[0079] Among alkaline water-soluble polymers having an acidic groupselected from the above-mentioned (1) to (6), alkaline water-solublepolymers having (1) a phenol group, (2) a sulfoneamide group and (3) anactive imide group are most preferable from the standpoints ofsolubility in an alkaline developing solution, developing latitude, andsufficient ensuring of film strength.

[0080] Examples of the alkaline water-soluble polymers having an acidicgroup selected from the above-mentioned (1) to (6) include the followingpolymers.

[0081] As the alkaline water-soluble polymer (1) having a phenol groupinclude novolak resins and polymers having a hydroxyaryl group as theside chain. Examples of the novolak resin include resins obtained bycondensing phenols with aldehydes under acidic condition.

[0082] Among them, preferable are, for example, novolak resins obtainedfrom phenol and formaldehyde, novolak resins obtained from m-cresol andformaldehyde, novolak resins obtained from p-cresol and formaldehyde,novolak resins obtained from o-cresol and formaldehyde, novolak resinsobtained from octylphenol and formaldehyde, novolak resins obtained fromm-/p-mixed cresol and formaldehyde, novolak resins obtained from aphenol/cresol (may be m-, p-, o- or m-/p-, m-/o-, o-/p-mixed type)mixture and formaldehyde, and the like.

[0083] The novolak resin is preferably selected from those having aweight-average molecular weight from 800 to 200000 and a number-averagemolecular weight from 400 to 60000.

[0084] Further, the above-mentioned polymers having a hydroxyaryl groupas the side chain are also preferable, and examples of the hydroxyarylgroup in this polymer include an aryl group to which one or more OHgroups are bonded.

[0085] Examples of the above-mentioned aryl group include, for example,a phenyl group, naphthyl group, anthracenyl group, phenanethrenyl groupand the like, and of them, a phenyl group or naphthyl group ispreferable from the standpoints of easy availability and physicalproperties.

[0086] Therefore, as the hydroxyaryl group, a hydroxyphenyl group,dihydroxyphenyl group, trihydroxyphenyl group, tetrahydroxyphenyl group,hydroxynaphthyl group, dihydroxynaphthyl group and the like arepreferable.

[0087] These hydroxyaryl groups may further have a substituent such as ahalogen atom, a hydrocarbon group having 20 or less carbon atom, analkoxy group having 20 or less carbon atom, an aryloxy group having 20or less carbon atoms or the like.

[0088] The hydroxyaryl group is bonded as the side chain in the form ofa pendant to the main chain constituting a polymer, and may also have aconnecting group between the main chain.

[0089] Examples of the polymer having a hydroxyaryl group as the sidechain which can be used in this embodiment include, for example,polymers having any one of constituent units of the following generalformulae (IX) to (XII). However, the scope of the present invention isnot limited to these examples.

[0090] In the general formulae (IX) to (XII), R¹¹ represents a hydrogenatom or methyl group. R¹² and R¹³ may be the same or different, andrepresent a hydrogen atom, a halogen atom, a hydrocarbon group having 10or less carbon atoms, an alkoxy group having 10 or less carbon atoms oran aryloxy group having 10 or less carbon atoms. R¹² and R¹³ may bebonded or ring-condensed to form a benzene ring or cyclohexane ring. R¹⁴represents a single bond or a divalent hydrocarbon group having 20 orless carbon atom. R¹⁵ represents a single bond or a divalent hydrocarbongroup having 20 or less carbon atom. R¹⁶ represents a single bond or adivalent hydrocarbon group having 10 or less carbon atom. X1 representsa single bond, ether bond, thioether bond, ester bond or amide bond. prepresents an integer from 1 to 4. Each of q and r independentlyrepresents an integer from 0 to 3.

[0091] Specific examples of constituent units of the above-mentionedgeneral formulae (IX) to (XII) include, but are not limited to, in thepresent invention, the following compounds.

[0092] Polymers containing the above-mentioned constituent units can besynthesized by a method appropriately selected from conventionally knownmethods.

[0093] A polymer having a constituent unit of the general formula (IX)can be obtained, for example, by radical-polymerizing oranion-polymerizing of a corresponding styrene derivative in which ahydroxyl group is protected as an acetate or t-butyl ether to obtain apolymer, then, de-protecting the polymer.

[0094] A polymer having a constituent unit of the general formula (X)can be synthesized, for example, by methods described in JP-A Nos.64-32256 and 64-35436.

[0095] A polymer having a constituent unit of the general formula (XI)can be obtained, for example, by reacting an amine compound having ahydroxyl group with maleic anhydride to obtain a corresponding monomer,then, radical-polymerizing the monomer to obtain a polymer.

[0096] A polymer having a constituent unit of the general formula (XII)can be obtained, for example, by deriving styrenes having a functionalgroup useful for synthesis such as chloromethylstyrene, carboxystyreneand the like as raw materials into a monomer corresponding to thegeneral formula (XII), and by further radical-polymerizing the monomerto form a polymer.

[0097] In these embodiments, homopolymers composed only of a constituentunit of the general formula (IX) to (XII) may be used, and also,copolymers containing other constituent units may be used.

[0098] Examples of the other constituent units include constituent unitsderived from known monomers such as acrylates, methacrylates,acrylamides, methacrylamides, vinyl esters, styrene, acrylic acid,methacrylic acid, acrylonitrile, maleic anhydride, maleic imide and thelike.

[0099] Examples of the above-mentioned acrylates include methylacrylate, ethyl acrylate, (n- or i-)propyl acrylate, (n-, i-, sec- ort-)butyl acrylate, amyl acrylate, 2-ethylhexyl acrylate, dodecylacrylate, chloroethyl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropylacrylate, 5-hydroxypentyl acrylate, cyclohexyl acrylate, allyl acrylate,trimethylolpropane monoacrylate, pentaerythritol monoacrylate, glycidylacrylate, benzyl acrylate, methoxybenzyl acrylate, chlorobenzylacrylate, 2-(p-hydroxyphenyl)ethyl acrylate, furfuryl acrylate,tetrahydrofurfuryl acrylate, phenyl acrylate, chlorophenyl acrylate,sulfamoylphenyl acrylate and the like.

[0100] Examples of the above-mentioned methacrylates include methylmethacrylate, ethyl methacrylate, (n- or i-)propyl methacrylate, (n-,i-, sec- or t-)butyl methacrylate, amyl methacrylate, 2-ethylhexylmethacrylate, dodecyl methacrylate, chloroethyl methacrylate,2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate,5-hydroxypentyl methacrylate, cyclohexyl methacrylate, allylmethacrylate, trimethylolpropane monomethacrylate, pentaerythritolmonomethacrylate, glycidyl methacrylate, methoxybenzyl methacrylate,chlorobenzyl methacrylate, 2-(p-hydroxyphenyl)ethyl methacrylate,furfuryl methacrylate, tetrahydrofurfuryl methacrylate, phenylmethacrylate, chlorophenyl methacrylate, sulfamoylphenyl methacrylateand the like are listed.

[0101] Examples of the above-mentioned acrylamides include acrylamide,N-methylacrylamide, N-ethylacrylamide, N-propylacrylamide,N-butylacrylamide, N-benzylacrylamide, N-hydroxyethylacrylamide,N-phenylacrylamide, N-tolylacrylamide, N-(p-hydroxyphenyl)acrylamide,N-(sulfamoylphenyl)acrylamide, N-(phenylsulfomyl)acrylamide,N-(tolylsulfonyl)acrylamide, N,N-dimethylacrylamide,N-methyl-N-phenylacrylamide, N-hydroxyethyl-N-methylacrylamide and thelike.

[0102] Examples of the above-mentioned methacrylamides includemethacrylamide, N-methylmethacrylamide, N-ethylmethacrylamide,N-propylmethacrylamide, N-butylmethacrylamide, N-benzylmethacrylamide,N-hydroxyethylmethacrylamide, N-phenylmethacrylamide,N-tolylmethacrylamide, N-(p-hydroxyphenyl)methacrylamide,N-(sulfamoylphenyl)methacrylamide, N-(phenylsulfomyl)methacrylamide,N-(tolylsulfonyl)methacrylamide, N,N-dimethylmethacrylamide,N-methyl-N-phenylmethacrylamide, N-hydroxyethyl-N-methylmethacrylamideand the like.

[0103] Examples of the above-mentioned vinylesters include vinylacetate, vinyl butyrate, vinyl benzoate and the like.

[0104] Examples of the above-mentioned styrenes include styrene,methylstyrene, dimethylstyrene, trimethylstyrene, ethylstyrene,propylstyrene, cyclohexylstyrene, chloromethylstyrene,trifluoromethylstyrene, ethoxymethylstyrene, acetoxymethylstyrene,methoxystyrene, dimethoxystyrene, chlorostyrene, dichlorostyrene,bromostyrene, iodostyrene, fluorostyrene, carboxystyrene and the like.

[0105] Of these monomers, acrylates, methacrylates, acrylamides,methacrylamides, vinyl esters, styrene, acrylic acid, methacrylic acid,acrylonitrile having 20 or less carbon atoms are preferable.

[0106] The proportion of constituent units of the general formulae (IX)to (XII) contained in a copolymer using the above-mentioned monomers ispreferably from 5 to 100% by weight, more preferably from 10 to 100% byweight.

[0107] The molecular weight of the polymer having a hydroxyaryl group asthe side chain is preferably 4000 or more, more preferably from 10000 to300000 in terms of weight-average molecular weight. The number-averagemolecular weight is preferably 1000 or more, more preferably from 2000to 250000. Further, degree of polydispersion (weight-average molecularweight/number-average molecular weight) is preferably or more, morepreferably from 1.1 to 10.

[0108] The polymer having a hydroxyaryl group as the side chain may beany of a random polymer, block polymer, graft polymer and the like, andamong them, a random polymer is preferable.

[0109] As the alkaline water-soluble polymer (2) having a sulfoneamidegroup, for example, polymers constituted, as the main constituentcomponent, of a minimum constituent unit derived from a compound havinga sulfoneamide group are listed. As the above-mentioned compound,compounds having, in the molecule, one or more sulfoneamide groups inwhich at least one hydrogen atom is bonded to a nitrogen atom and one ormore polymerizable unsaturated bonds, are listed. Among other, lowermolecular weight compounds having in the molecule an acryloyl group,allyl group or vinyloxy group, and a substituted or mono-substitutedaminosulfonyl group or a substituted sulfonylimino group are preferable,and for example, compounds of the following general formulae 1 to 5 arelisted.

[0110] [wherein, each of X¹ and X² independently represents —O— or—NR²⁷—. Each of R²¹ and R²⁴ independently represents a hydrogen atom or—CH₃. Each of R²², R²⁵, R²⁹, R³² and R³⁶ independently represents analkylene group having 1 to 12 carbon atoms optionally having asubstituent, a cycloalkylene group, an arylene group or an aralkylenegroup. Each of R²³, R²⁷ and R³³ independently represents a hydrogenatom, an alkyl group having 1 to 12 carbon atoms and which may have asubstituent, a cycloalkyl group, an aryl group or an aralkyl group.Further, each of R²⁶ and R³⁷ independently represents an alkyl grouphaving 1 to 12 carbon atoms and which may have a substituent, acycloalkyl group, an aryl group or an aralkyl group. Each of R²⁸, R³⁰and R³⁴ independently represents a hydrogen atom of —CH₃. Each of R³¹and R³⁵ independently represents a single bond, or an alkyl group having1 to 12 carbon atoms and which may have a substituent, a cycloalkylenegroup, an arylene group or an aralkylene group. Each of Y³ and Y⁴independently represents a single bond, or —CO—.].

[0111] Among compounds of the general formulae 1 to 5,m-aminosulfonylphenyl methacrylate,N-(p-aminosulfonylphenyl)methacrylamide,N-(p-aminosulfonylphenyl)acrylamide and the like can be suitably used,in the negative planographic printing material of the present invention.

[0112] Examples of the alkaline water-soluble polymer (3) having anactive imide group include polymers formed of a minimum constituent unitderived from a compound having an active imide group as the mainconstituent component. Examples of the above-mentioned compound arecompounds having, in the molecule, one or more active imide groups ofthe following structural formula and one or more polymerizableunsaturated bonds.

[0113] Specifically, N-(p-toluenesulfonyl)methacrylamide,N-(p-toluenesulfonyl)acrylamide and the like can be suitably used.

[0114] Examples of the alkaline water-soluble polymer (4) having acarboxyl group include polymers formed of a minimum constituent unitderived from a compound having, in the molecule, one or more carboxylgroups and one or more polymerizable unsaturated groups as the mainconstituent component.

[0115] Example of the alkaline water-soluble polymer (5) having asulfonic group, for example, polymers formed of a minimum constituentunit derived from a compound having, in the molecule, one or moresulfonic groups and one or more polymerizable unsaturated groups, as themain constituent component.

[0116] As the alkaline water-soluble polymer (6) having a phosphategroup, for example, polymers constituted, as the main constituentcomponent, of a minimum constituent unit derived from a compound having,in the molecule, one or more phosphate groups and one or morepolymerizable unsaturated groups are listed.

[0117] These alkali water-soluble polymers preferably further have aradical polymerizable ethylenic double bond on the main chain or sidechain thereof. It is preferable that an ethylene group, acryloyloxygroup, methacryloyloxy group and vinyl group are contained as theethylenic double bond.

[0118] The minimum constituent unit having an acidic group selected fromthe above-mentioned (1) to (6) forming an alkaline water-soluble polymerused in a material for the negative planographic printing plate of thepresent invention is not necessarily restricted to one kindspecifically, and those obtained by copolymerizing two or more minimumconstituent units having the same acidic group or two or more minimumconstituent units having different acidic groups can also be used.

[0119] As the method of copolymerization, a graft copolymerizationmethod, block copolymerization method, random copolymerization methodand the like which are conventionally known can be used.

[0120] In the above-mentioned polymers, compounds having an acidic groupselected from (1) to (6) to be copolymerized are contained in thecopolymer in an amount of preferably 10 mol % or more, more preferably20 mol % or more. When less than 10 mol %, there is a tendency thatdeveloping latitude can not be sufficiently improved.

[0121] In the present invention, when compounds are copolymerized toform a copolymer, other compounds not containing the above-mentionedacidic groups (1) to (6) can also be used as the compounds. Examples ofthe other compounds not containing the above-mentioned acidic groups (1)to (6) are compounds as listed in the following (m1) to (m11).

[0122] (m1): For example, acrylates and methacrylates having analiphatic hydroxyl group such as 2-hydroxyethyl acrylate or2-hydroxyethyl methacrylate and the like.

[0123] (m2): Alkyl acrylates such as methyl acrylate, ethyl acrylate,propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, octylacrylate, benzyl acrylate, 2-chloroethyl acrylate, glycidyl acrylate,N-dimethylamylethyl acrylate and the like.

[0124] (m3): Alkyl methacrylates such as methyl methacrylate, ethylmethacrylate, propyl methacrylate, butyl methacrylate, amylmethacrylate, hexyl methacrylate, cyclohexyl methacrylate, benzylmethacrylate, 2-chloroethyl methacrylate, glycidyl methacrylate,N-dimethylamylethyl methacrylate and the like.

[0125] (m4): Acrylamides or methacrylamides such as acrylamide,methacrylamide, N-methylolacrylamide, N-ethylacrylamide,N-hexylmethacrylamide, N-cyclohexylacrylamide, N-hydroxyethylacrylamide,N-phenylacrylamide, N-nitrophenylacrylamide, N-ethyl-N-phenylacrylamideand the like.

[0126] (m5): Vinyl ethers such as ethyl vinyl ether, 2-chloroethyl vinylether, hydroxyethyl vinyl ether, propyl vinyl ether, butyl vinyl ether,octyl vinyl ether, phenyl vinyl ether and the like.

[0127] (m6): Vinyl esters such as vinyl acetate, vinylchloro acetate,vinyl butyrate, vinyl benzoate and the like.

[0128] (m7): Styrenes such as styrene, α-methylstyrene, methylstyrene,chloromethylstyrene and the like.

[0129] (m8): Vinyl ketones such as methyl vinyl ketone, ethyl vinylketone, propyl vinyl ketone, phenyl vinyl ketone and the like.

[0130] (m9): Olefins such as ethylene, propylene, isobutylene,butadiene, isoprene and the like.

[0131] (m10): N-vinylpyrrolidone, N-vinylcarbazole, 4-vinylpyridine,acrylonitrile, methacrylonitrile and the like.

[0132] (m11): Unsaturated imides such as maleimide,N-acryloylacrylamide, N-acetylmethacrylamide, N-propionylmethacrylamide,N-(p-chlorobenzoyl)methacrylamide and the like.

[0133] As the alkali water-soluble polymer used in the planographicprinting plate of the present invention, those having a weight-averagemolecular weight of 2000 or more and a number-average molecular weightof 500 or more are preferable from the standpoints of sensitivity anddevelopment latitude, irrespective of whether they are homopolymers orcopolymers, and further preferable are those having a weight-averagemolecular weight of from 5000 to 300000 and a number-average molecularweight of from 800 to 250000. Further, those having a degree ofpolydispersion (weight-average molecular weight/number-average molecularweight) of 1.1 to 10 are preferable.

[0134] When a copolymer is used in the present invention, thecompounding weight ratio of a minimum constituent unit derived from acompound having an acidic group selected from the above-mentioned (1) to(6) which form the main chain and/or side chain thereof to a minimumconstituent unit containing no acidic group of the (1) to (6) which formpart of the main chain and/or side chain is preferably from 50:50 to5:95, more preferably from 40:60 to 10:90 from the standpoint of effect.

[0135] The above-mentioned alkali water-soluble polymers may be usedeach alone or in combination of two or more.

[0136] Further, urethane-based binder polymers containing an acidicgroup described in JP-BNos. 7-12004,7-120041, 7-120042, 8-12424, JP-ANos. 63-287944, 63-287947, 1-271741, 10-116232 and the like are veryexcellent in strength, and consequently, advantageous from thestandpoints of printing endurance and low exposure suitability.

[0137] Further, in addition to the above-mentioned polymers,polyvinylpyrrolidone and polyethylene oxide and the like are useful asthe water-soluble linear organic polymer. For enhancing the strength ofa hardened film, alcohol-soluble nylon, polyether of2-bis-(4-hydroxyphenyl)-propane and epichlorohydrin, and the like arealso useful.

[0138] The weight-average molecular weight of a polymer used in thepresent invention is preferably 5000 or more, further preferably from10000 to 300000, and the number-average molecular weight is preferably1000 or more, further preferably from 2000 to 250000. The degree ofpolydispersion (weight-average molecular weight/number-average molecularweight) is preferably 1 or more, further preferably from 1.1 to 10.

[0139] These polymers maybe any of a random polymer, block polymer,graft polymer and the like, and, a random polymer is preferable.

[0140] The binder polymer used in the present invention may be usedalone or in admixture. These polymers are added into a recording layerin a proportion of 20 to 95% by weight, and preferably 30 to 90% byweight based on the total amount of all solid components in a recordinglayer application solution. In the case of an addition amount of lessthan 20% by weight, when an image is formed, the strength of imageportion is impaired. In the case of an addition amount of over 95% byweight, an image is not formed. The weight ratio of a radicalpolymerizable compound having an ethylenically unsaturated double bondto a linear organic polymer is preferably from 1/9 to 7/3.

[0141] As the materials which form the recording layer of the presentinvention, various additives can be used together, if necessary, inaddition to the above-mentioned compounds.

[0142] For example, thermally decomposable compounds such as oniumsalts, aromatic sulfonates and the like described as “other components”which can be added to a positive photosensitive composition in paragraphnumber [0067] and those following in JP-A No. 11-174681 are suitable forcontrolling an ability to inhibit dissolving of image portion, andadditionally, additives useful for improving sensitivity such as cyclicacid anhydrides, phenols, organic acids and the like, surfactants,printing agents, dyes as an image coloring agent, pigments and the likedescribed as “other components” in the same publication can also be usedlikewise in the present invention. Further, epoxy compounds, vinyl ethercompounds, further, phenol compounds having a hydroxymethyl groupdescribed in JP-A No. 8-276558, crosslinkable compounds having an alkalidissolving suppressing action described in JP-A No. 11-160860, and thelike can also be added appropriately according to the object.

[0143] Other Components

[0144] Various compounds may also be added to a recording layer in thepresent invention, if necessary, in addition to the above-mentionedcompound. For example, dyes manifesting large absorption in a visiblelight region can be used as an image-coloring agent. Further, pigmentssuch as phthalocyanine-based pigments, azo-based pigments, carbon black,titanium oxide and the like can also be suitably used.

[0145] It is preferable to add these coloring agents to facilitatediscrimination between image portions and non-image portions afterformation of images. The addition amount thereof is from 0.01 to 10% byweight based on the total amount of all solid components in a recordinglayer application solution.

[0146] Further, in the present invention, when the recording layer is aphotopolymerizable layer, it is desirable to add a small amount of aheat polymerization inhibitor for inhibiting unnecessary heatpolymerization of a radical polymerizable compound having anethylenically unsaturated double bond during preparation or storage ofan application solution. As the suitable heat polymerization inhibitingagent, hydroquinone, p-methoxyphenol, di-t-butyl-p-cresol, pyrogallol,t-butylcatechol, benzoquinone, 4,4′-thiobis(3-methyl-6-t-butylphenol),2,2′-methylenebis(4-methyl-6-t-butylphenol),N-nitroso-N-phenylhydroxylamine aluminum salt and the like are listed.The amount of a heat polymerization inhibiting agent added is preferablyfrom about 0.01% by weight to about 5% by weight based on the weight ofthe whole composition. If necessary, higher fatty acid derivatives suchas behenic acid and behenic amide may be added to prevent polymerizationinhibition by oxygen, or it may be allowed to locally exist on thesurface of a recording layer in a process of drying after application.The addition amount of a higher fatty acid derivative is preferably fromabout 0.1% by weight to about 10% by weight based on the wholecomposition.

[0147] Further, in a recording layer application solution in the presentinvention, nonionic surfactants as described in JP-A No. 62-251740 and3-208514, and ampholytic surfactants as described in JP-A Nos. 59-121044and 4-13149 can be added, for increasing stability of treatment withrespect to development conditions.

[0148] Moreover, in a recording layer application solution in thepresent invention, a plasticizer is added, if necessary, for impartingflexibility of a film and the like. For example, polyethylene glycol,tributyl citrate, diethyl phthalate, dibutyl phthalate, dihexylphthalate, dioctyl phthalate, tricresyl phosphate, tributyl phosphate,trioctyl phosphate, tetrahydrofurfuryl oleate and the like are used.

[0149] For producing the planographic printing plate of the presentinvention, it may be usually advantageous that the above-mentionedcomponents necessary for a recording layer application solution aredissolved in a solvent to prepare a solution which is applied on asuitable substrate. Examples of the solvent herein used include, but notlimited to, ethylene dichloride, cyclohexanone, methyl ethyl ketone,methanol, ethanol, propanol, ethylene glycol monomethyl ether,1-methoxy-2-propanol, 2-methoxy ethyl acetate, 1-methoxy-2-propylacetate, dimethoxyethane, methyl lactate, ethyl lactate,N,N-dimethylacetamide, N,N-dimethylformamide, tetramethylurea,N-methylpyrrolidone, dimethylsulfoxide, sulfolane, γ-butyrolactone,toluene, methyl isobutyl ketone, hydrogen and the like. These solventsare used alone or in admixture. The concentration of the above-mentionedcomponents (all solid components including additives) in a solvent ispreferably from 1 to 50% by weight.

[0150] Regarding the amount of this recording layer applied, theapplication amount of a polymer layer (solid component) on a substrateobtained after application and drying varies depending on use, Lut ispreferably from 0.1 to 5.0 g/m² in general, in the case of use as aplanographic printing plate, though it varies depending on use.

[0151] As the application method, various methods can be used, and forexample include bar coater application, rotation application, sprayapplication, curtain application, dip application, air knifeapplication, blade application, roll application and the like.

[0152] Substrate

[0153] The substrate is a dimensionally stable plate, and there arelisted, for example, paper, paper laminated with plastics (for example,polyethylene, polypropylene, polystyrene and the like), metal plates(for example, aluminum, zinc, copper and the like), and plastic films(for example, cellulose diacetate, cellulose triacetate, cellulosepropionate, cellulose butyrate, cellulose acetate butyrate, cellulosenitrate, polyethylene terephthalate, polyethylene, polystyrene,polypropylene, poycarbonate, polyvinyl acetal and the like), paper orplastic films laminated or vapor-deposited with metals as describedabove, and the like.

[0154] As the substrate used in the present invention, polyester filmsor aluminum plates are preferable, and of them, an aluminum plate whichhas excellent dimension stability and is relatively cheap isparticularly preferable. The suitable aluminum plate is a pure aluminumplate or an alloy which is plate composed mainly of aluminum andcontains a trace amount of foreign elements, and further, plastic filmslaminated or deposited with aluminum may also be used. As the foreignelements contained in an aluminum alloy, silicon, iron, manganese,copper, magnesium, chromium, zinc, bismuth, nickel, titanium and thelike are listed. The content of the foreign elements in the alloy is atmost 10% by weight or less. In the present invention, particularlysuitable aluminum is pure aluminum, however, since completely purealuminum is not produced easily from the standpoint of refiningtechnology, those containing a trace amount of foreign elements may alsobe used. The aluminum plate thus applied to the present invention doesnot have a formulation limited within a specific range, andaluminumplates made of conventionally known and used materials can beappropriately utilized.

[0155] The thickness of the above-mentioned aluminum plate is from about0.1 to 0.6 mm, preferably from 0.15 to 0.4 mm, particularly preferablyfrom 0.2 to 0.3 mm.

[0156] An aluminum plate is roughened before used, and prior toroughening, if required, de-greasing treatment is conducted using asurfactant, organic solvent or alkaline aqueous solution and the like,for example, for removing a drawing oil on the surface.

[0157] The surface roughening treatment of the surface of an aluminumplate is conducted by various methods, and for example, a mechanicalroughening method, a method of solving and roughening the surfaceelectrochemically, and a method of selectively solving the surface, areused. As the mechanical method, known methods such as a ball polishingmethod, brush polishing method, buff polishing method and the like canbe used. As the electrochemical roughening method, methods usingalternating current or direct current in a hydrochloric acid or nitricacid electrolyte solution are used. Further methods using bothhydrochloric acid and nitric acid electrolyte solutions in combinationcan also be used as disclosed in JP-A No. 54-63902.

[0158] An aluminum plated thus roughened can be subjected, if necessary,to alkali etching treatment and neutralization treatment, then, forenhancing water-retention and abrasion-resistance of the surface, toanodizing treatment, if desired. As the electrolytes used for anodizingtreatment of an aluminum plate, various electrolytes forming a porousoxide film can be used, and in general, sulfuric acid, phosphoric acid,oxalic acid, chromic acid or a mixed acid thereof can be used. Theconcentrations of these electrolytes are appropriately determineddepending on the kinds of the electrolytes.

[0159] The treating conditions for anodizing can not universally bespecified since they change variously depending on electrolytes used,and in general, it is suitable that the concentration of electrolytes isfrom 1 to 80% by weight based on the solution, the liquid temperature isfrom 5 to 70° C., the current density is from 5 to 60 A/dm², the voltageis from 1 to 100 V, and the electrolysis time is from 10 seconds to 5minutes. If the amount of an anodized film is less than 1.0 g/m²,printing endurance is insufficient, non-image portions of a planographicprinting plate are scratched easily. Consequently, so-called “scratchstaining” in which ink is adhered to scratched parts in printing tendsto occur.

[0160] After anodizing treatment, hydrophilization treatment isperformed, if necessary, on the surface of aluminum. As suchhydrophilization treatment used in the present invention, an alkalimetal silicate (for example, sodium silicate aqueous solution) method asdisclosed in U.S. Pat. Nos. 2,714,066, 3,181,461, 3,280,734 and3,902,734 is used. In this method, a substrate is immersed in a sodiumsilicate aqueous solution or subjected to electrolysis treatment. Inaddition, methods of treatment with potassium fluorozirconate disclosedin JP-B No. 36-22063, and polyvinylphosphonic acid disclosed in U.S.Pat. Nos. 3,276,868, 4,153,461 and 4,689,272, and other methods areused.

[0161] A primer layer can also be provided, if necessary, between asubstrate and a polymer layer. Various organic compounds are used as acomponent of a primer layer, and selected from, for example, phosphonicacids having an amino group such as carboxymethylcellulose, dextrin, gumArabic, 2-aminoethylphosphonic acid and the like; organic phosphonicacids such as phenylphosphonic acid optionally having a substituent,naphthylphosphonic acid, alkylphosphonic acid, glycerophosphonic acid,methylenediphosphonic acid, ethylenediphosphonic acid and the like;organic phosphoric acids such as phenylphosphoric acid optionally havinga substituent, naphthylphosphoric acid, alkylphosphoric acid andglycerophosphoric acid and the like; organic phosphinic acids such asphenylphosphinic acid optionally having a substituent,naphthylphosphinic acid, alkylphosphinic acid, glycerophosphinic acidand the like; amino adis such as glycine, β-alanine and the like;hydrochlorides of amines having a hydroxyl group such as a hydrochlorideof triethanolamine and the like, and they may also be mixed and used.

[0162] Further, in the present invention, a polyfunctional aminecompound can also be added to a primer layer as described above. In thiscase, a primer layer may be formed together with the above-mentionedother organic compounds, or a primer layer may be formed only of apolyfunctional amine compound.

[0163] The coating amount of a primer layer is suitably from 2 to 200mg/m², and preferably from 5 to 100 mg/m². When the above-mentionedcoating amount is less than 2 mg/m², sufficient printing endurance maynot be obtained. The same tendency arises also when the coating amountis over 200 mg/m².

[0164] The produced planographic printing plate is usually subjected toimage-wise exposure and development treatment, to produce a plate.

[0165] The light source of the active beam used in the image-wiseexposure is preferably a light source having a light emitting wavelengthin a near infrared to infrared region, and solid laser and semiconductorlaser are particularly preferable. For locally controlling the filmhardness of a recording layer which is a characteristic of theplanographic printing plate of the present invention, control of filmhardness can be conducted more effectively by controlling the outputenergy of infrared laser used in this exposure, and consequentlycontrolling light quantity of laser which can reach deeper portions, inaddition to the above-mentioned control of the optical density of arecording layer.

[0166] Developer

[0167] As the developer and replenisher used in development of theplanographic printing plate of the present invention, conventionallyknown alkali developers containing the following components can be used,and preferably, those manifesting low permeability into a recordinglayer after hardening are used.

[0168] The extent of permeability into this recording layer can bedetected by change of electrostatic capacity. An example of the methodof measuring electrostatic capacity which indicates permeability in thepresent invention is one in which an aluminum substrate carrying thereona hardened recording layer is immersed as one electrode in a developer,a conductor is connected to the aluminum substrate, and a usualelectrode is used as another electrode, and voltage is applied, as shownin FIG. 1. When the voltage is applied initially, a recording layerfunctions as an insulation layer and electrostatic capacity does notchange. However, with the lapse of immersion time, a developer permeatesinto the interface between a substrate and a recording layer, and theelectrostatic capacity changes. When time until this change inelectrostatic capacity is long, permeability is judged to be low.

[0169]FIG. 2 is a graph showing a relation between immersion time(voltage application time) and electrostatic capacity. Time t_(s)represents time of usual development conducted using an automaticdeveloping machine. In a graph A represented by solid line, time t_(A)is required for a change in electrostatic capacity to take place, and islonger than usual development time T_(s). Therefore, in usualdevelopment, damage of hardened image portions and decrease in printingendurance do not occur. On the other hand, in a graph B represented bythe broken line, only time t_(B) is necessary for the in electrostaticcapacity to change, and it is shorter than usual development time t_(s).Therefore, it is estimated that, in usual development, a developerpermeates into the interface between a substrate and a recording layer,to cause reduction in close adherence at the interface, thus causingpeeling of image portions.

[0170] Since usual development time t_(s) is from about 5 seconds toabout 60 seconds, it is preferable to use a developer having suchpermeability that time required until change in electrostatic capacityis 60 seconds or more, and preferably 90 seconds or more.

[0171] Such control of permeability can be conducted by regulating thecompounding amount of components of a developer which are listed below.

[0172] Components usually used in a developer will be described below.

[0173] Alkali Agent

[0174] The developer and development replenisher used in development inthe method of producing a planographic printing plate of the presentinvention are an alkali aqueous solution having a pH of from 9.0 to13.5, more preferably from 10.0 to 13.3.

[0175] As such developer and development replenisher, conventionallyknown alkali aqueous solutions can be used. For example, organic alkaliagents such as sodium silicate, potassium silicate, sodium tertiaryphosphate, potassium tertiary phosphate, ammonium tertiary phosphate,sodium secondary phosphate, potassium secondary phosphate, ammoniumsecondary phosphate, sodium bicarbonate, potassium bicarbonate, ammoniumbicarbonate, sodium carbonate, potassium carbonate, ammonium carbonate,sodium hydrogen carbonate, potassium hydrogen carbonate, ammoniumhydrogen carbonate, sodium borate, potassium borate, ammonium borate,sodium hydroxide, ammonium hydroxide, potassium hydroxide and lithiumhydroxide, and the like can be used. Further, organic alkali agents suchas monomethylamine, dimethylamine, trimethylamine, monoethylamine,diethylamine, triethylamine, monoisopropylamine, diisopropylamine,triisopropylamine, n-butylamine, monoethanolamine, diethanolamine,triethanolamine, monoisopropanolamine, diisopropanolamine,ethyleneimine, ethylenediamine, pyridine and the like are also used.

[0176] Of these alkali agents, preferable are aqueous solutions ofsilicates such as sodium silicate, potassium silicate and the like. Thereason for this is that controlling pH and developing property arepossible by regulating the ratio of silicon oxide Sio₂ which is acomponent of a silicate to an alkali metal oxide M₂O (generallyrepresented by [SiO₂]/[M₂O] molar ratio) and by regulatingconcentration. For example, an alkali metal silicate composed of anaqueous solution of potassium silicate having a SiO₂/K₂O molar ratio of0.5 to 2.0 (namely, [SiO₂]/[K₂O] is 0.5 to 2.0) and a SiO₂ content of 1to 4% by weight is suitably used in the present invention.

[0177] Further, examples of other preferable alkali agents includebuffer solutions composed of a weak acid and strong base are listed. Asthe weak acid used in such buffering solutions, those having an aciddissociation constant (pKa) of 10.0 to 13.3 are preferable, andparticularly, those having a pKa of 11.0 to 13.1 are preferable. In thecase, for example, of sulfosalicylic acid, tertiary dissociationconstant is 11.7, and it can be suitably used in the present invention.Namely, a polybasic acid, can be used in the present invention providingat least one acid dissociation constant is within the above-mentionedrange.

[0178] Such a weak acid is selected from those described in PergamonPress, IONISATION CONSTANTS OF ORGANIC ACIDS INAQUEOUS SOLUTION, and thelike, and examples include alcohols such as2,2,3,3-tetrafluoropropanol-1 (pKa 12.74), trifluoroethanol (pKa 12.37),trichloroethanol (pKa 12.24) and the like; aldehydes such aspydirine-2-aldehyde (pKa 12.68), pydirine-4-aldehyde (pKa 12.05) and thelike; saccharides such as sorbitol (pKa 13.0), saccharose (pKa 12.7),2-deoxyribose (pKa 12.61), 2-deoxyglucose (pKa 12.51), glucose (pKa12.46), galactose (pKa 12.35), arabinose (pKa 12.34), xylose (pKa12.29), fructose (pKa 12.27), ribose (pKa 12.22), mannose (pKa 12.08),L-ascorbic acid(pKa 11.34) and the like; compounds having a phenolichydroxyl group such as salicylic acid (pKa 13.0), 3-hydroxy-2-naphtoicacid (pKa 12.84), catechol (pKa 12.6), gallic acid (pKa 12.4),sulfosalicylic acid (pKa 11.7), 3,4-dihydroxysulfonic acid (pKa 12.2),3,4-dihydroxybenzoic acid (pKa 11.94), 1,2,4-trihydroxybenzene (pKa11.82), hydroquinone (pKa 11.56), pyrogallol (pKa 11.34), resorcinol(pKa 11.27) and the like; oximes such as 2-butanoneoxime (pKa 12.45),acetoxime (pKa 12.42), 1,2-cycloheptanedionedioxime (pKa 12.3),2-hydroxybenzaldehydeoxime (pKa 12.10), dimethylglyoxime (pKa 11.9),ethanediamidedioxime (pKa 11.37), acetophenoneoxime (pKa 11.35) and thelike; amino acids such as 2-quinolone (pKa11.76), 2-pyridone (pKa11.65),4-quinolone (pKa 11.28), 4-pyridone (pKa 11.12), 5-aminovaleric acid(pKa 10.77), 2-mercaptoquinoline (pKa 10.25), 3-aminopropionic acid (pKa10.24) and the like; nucleic acid associated substances such asfluorouracil (pKa 13.0), guanosine (pKa 12.6), uridine (pKa 12.6),adenosine (pKa 12.56), inosine (pKa 12.5), guanine (pKa 12.3), cytidine(pKa 12.2), cytosine (pKa 12.2), hypoxanthin (pKa 12.1), xanthin (pKa11.9) and the like; and in addition, weak acids such asdiethylaminomethylphosphonic acid (pKa 12.32),1-amino-3,3,3-trifluorobenzoic acid (pKa 12.29),isopropylidenediphosphonic acid (pKa 12.10), 1,1-ethylidenediphosphonicacid (pKa 11.54), 1-hydroxy 1,1-ethylidenediphosphonate (pKa 11.52),benzimidazole (pKa 12.86), thiobenzamide (pKa 12.8), picolinethioamide(pKa 12.55), barbituric acid (pKa 12.5) and the like.

[0179] As the strong base to be combined with these weak acids, sodiumhydroxide, ammonium hydroxide, potassium hydroxide and lithium hydroxideare used.

[0180] These alkali agents are used alone or in combination of two ormore. Among these alkali buffering agents, preferable are those obtainedby combining sulfosalicylicacid, salicylicacid, saccharose and sorbitolwith sodium hydroxide and potassium hydroxide. Among others, apreferable combination is sorbitol with potassium hydroxide or sodiumhydroxide.

[0181] The pH of the above-mentioned various alkali agents is controlledwithin a preferable range by concentration and combination, before usethereof.

[0182] When organic amines are used as the organic alkali agent, the useamount thereof used is preferably 1% by weight or less from thestandpoint of appropriate permeability.

[0183] Surfactant

[0184] To the developer and replenisher used in the present invention,various surfactants and organic solvents can be added, if necessary, forthe purpose of promoting developing property, dispersing developmentforeign matters, and enhancing ink affinity of printed image portions.Preferable surfactants are anionic, cationic, nonionic and ampholyticsurfactants.

[0185] As preferable examples of the surfactant, there are listednonionic surfactants such as polyoxyethylene alkyl ethers,polyoxyethylene alkylphenyl ethers, polyoxyethylene polystyrylphenylethers, polyoxyethylene polyoxypropylenealkyl ethers, glycerin fattyacid partial esters, sorbitan fatty acid partial esters, pentaerythritolfatty acid partial esters, propylene glycol monofatty esters, saccharosefatty acid partial esters, polyoxyethylene sorbitan fatty acid partialesters, polyoxyethylene sorbitol fatty acid partial esters, polyethyleneglycol fatty esters, polyglycerin fatty acid partial esters,polyoxyethylenized castor oils, polyoxyethylene glycerin fatty acidpartial esters, fatty acid diethanolamides,N,N-bis-2-hydroxyalkylamines, polyoxyethylenealkylamine,triethanolaminefatty esters, trialkylamine oxides and the like; anionicsurfactants such as fatty acid salts, abietic acid salts,hydroxyalkanesulfonic acid salts, alkanesulfonic acid salts,dialkylsulfosuccinate salts, alkylnaphthalenesulfonic acid salts,alkylphenoxypolyoxyethylenepropylsulfonic acid salts, polyoxyethyleneakylsulfophenyl ether salts N-methyl-N-oleyltaurin sodium salt,N-alkylsulfosuccinic monoamide disodium salts, petroleum sulphonic acidsalts, sulfated beef tallow oil, sulfate salts of fatty acid alkylesters, alkyl sulfate salts, polyoxyethylene alkyl ether sulfate salts,fatty monoglyceride sulfate salts, polyoxyethylene alkylphenyl ethersulfate salts, polyoxyethylene styrylphenyl ether sulfate salts,alkylphosphate salts, polyoxyethylene alkyl ether phosphate salts,polyoxyethylene alkylphenyl ether phosphate salts, partial saponifiedsubstances of styrene/maleic anhydride copolymers, partial saponifiedsubstances of olefin/maleic anhydride copolymers, naphthalenesulfonicacid salt formalin condensates and the like; cationic surfactants suchas alkylamine salts, quaternary ammonium salts such astetrabutylammonium bromide and the like, polyoxyethylenealkylaminesalts, polyethylenepolyamine derivatives and the like; and ampholyticsurfactants such as carboxybetaines, aminocarboxylic acids,sulfobetaines, aminosulfates, imidazolines and the like. of theabove-listed surfactants, the polyoxyethylene can also be regarded aspolyoxyalkylenes such as polyoxymethylene, polyoxypropylene,polyoxybutylene and the like, and surfactants thereof are also included.

[0186] Further preferable surfactants are fluorine-based surfactantscontaining a perfluoroalkyl group in the molecule. Examples of such afluorine-based surfactant are anionic surfactants such asperfluoroalkylcarboxylic acid salts, perfluoroalkylsulfonic acid salts,perfluoroalkylphosphates and the like; ampholytic surfactants such asperfluoroalkylbetaine and the like; cationic surfactants such asperfluoroalkyltrimethylammonium salts and the like; and nonionicsurfactants such as perfluoroalkylamine oxide, perfluoroalkyl ethyleneoxide adducts, perfluoroalkyl group and hydrophilic group-containingoligomers, perfluoroalkyl group and lipophilic group-containingoligomers, pefluoroalkyl group, hydrophilic group and lipophilicgroup-containing oligomers, perfluoroalkyl group and lipophilicgroup-containing urethane, and the like.

[0187] The above-mentioned surfactants can be used alone or incombination of two or more, and added into a developer in an amount of0.001 to 10% by weight, more preferably of 0.01 to 5% by weight.

[0188] Development Stabilizer

[0189] In the developer and replenisher used in the present invention,various development stabilizer are used, and as preferable examplesthereof are polyethylene glycol adducts of sugar alcohol described inJP-B No. 6-282979, tatraalkylammonium salts such as tetrabutylammoniumhydroxide and the like, phosphonium salts such as tetrabutylphosphoniumbromide and the like, and iodonium salts such as diphenyl iodoniumchloride and the like.

[0190] Further, there are anionic surfactants or ampholytic surfactantsdescribed in JP-A No. 50-51324, water-soluble cationic polymersdescribed in JP-A No. 55-95946, and water-soluble ampholytic polymerelectrolytes described in JP-A No. 56-142528.

[0191] Further, other examples include organic boron compounds havingalkylene glycol added described in JP-A No. 59-84241, water-solublesurfactants of polyoxyethylene, polyoxypropylene block polymer typedescribed in JP-A No. 60-111246, alkylenediamine compounds obtained bysubstitution of polyoxyethylene-polyoxypropylene described in JP-A No.60-129750, polyethylene glycols having a weight-average molecular weightof 300 or more described in JP-A No. 61-215554, fluorine-containingsurfactants having a cationic group described in JP-A No. 63-175858,water-soluble ethylene oxide adducts obtained by addition of 4 or moremol of ethylene oxides to an acid or alcohol described in JP-A No.2-39157, water-soluble polyalkylene compounds and the like.

[0192] Organic Solvent

[0193] To the developer and replenisher, an organic solvent is added ifnecessary. As such an organic solvent, those having a solubility inwater of about 10% by weight or less are suitable, and it is preferablyselected from those having a solubility in water of about 5% by weightor less. Example include 1-phenylethanol, 2-phenylethanol,3-phenyl-1-propanol, 4-phenyl-1-butanol, 4-phenyl-2-butanol,2-phenyl-1-butanol, 2-phenoxyethanol, 2-benzyloxyethanol,o-methoxybenzyl alcohol, m-methoxybenzyl alcohol, p-methoxybenzylalcohol, benzyl alcohol, cyclohexanol, 2-methylcyclohexanol,3-methylcyclohexanol and 4-methylcyclohexanol, N-phenylethanolamine,N-phenyldiethanolamine and the like. The content of an organic solventis from 0.1 to 5% by weight based on the total weight after used. Theamount thereof used has a close relation ship with the use amount of asurfactant used, and it is preferable to allow the amount of asurfactant to increase when the amount of an organic solvent increases.The reason for this is that when the amount of a surfactant is small,and a large amount of an organic solvent is used, the organic solvent isnot dissolved completely. Consequently, excellent developing propertycan not be secured.

[0194] Reducing Agent

[0195] To the developer and replenisher used in the present invention, areducing agent is further added. This prevents pollution of a printingplate, and is effective particularly in developing a negativephotosensitive planographic printing plate containing a photosensitivediazonium salt compound. Examples of preferable organic reducing agentinclude phenol compounds such as thiosalicylic acid, hydroquinone,methol, methoxyquinone, resorcin, 2-methylresorcin and the like, andamine compounds such as phenylenediamine, phenylhydrazine and the like.Examples of further preferable inorganic reducing agents include sodiumsalts, potassium salts and ammonium salts of inorganic acids such assulfurous acid, hydrogensulfite, phosphorous acid, hydrophosphorousacid, dihydrophosphorous acid, thiosulfuric acid, dithionous acid andthe like. Of these reducing agents, a sulfite has a particularlyexcellent contamination prevention effect. The reducing agents arecontained preferably in an amount of 0.05 to 5% by weight based on adeveloper in use.

[0196] Organic Carboxylic Acid

[0197] To the developer and replenisher used in the present invention,also an organic carboxylic acid can further be added. Preferable arealiphatic carboxylic acids and aromatic carboxylic acids having 6 to 20carbon atoms. As the specific examples of the aliphatic carboxylic acid,capronic acid, enanthylic acid, caprylic acid, laurylic acid, myrysticacid, palmitic acid, stearic acid and the like, and alkanic acids having8 to 12 carbon atoms are particularly preferable. Any of unsaturatedfatty acids having a double bond in a carbon chain or branched carbonchains is permissible.

[0198] The aromatic carboxylic acid is a compound obtained bysubstitution of a carboxyl group on a benzene ring, naphthalene ring,anthracene ring or the like, and specific examples thereof includeo-chlorobenzoic acid, p-chlorobenzoic acid, o-hydroxybenzoic acid,p-hydroxybenzoic acid, o-aminobenzoic acid, p-aminobenzoid acid,2,4-dihydroxybenzoic acid, 2,5-dihydroxybenzoic acid,2,6-dihydroxybenzoic acid, 2,3-dihydroxybenzoicacid,3,5-dihydroxybenzoicacid, gallic acid, 1-hydroxy-2-naphtoic acid,3-hydroxy-2-naphtoic acid, 2-hydroxy-1-naphtoic acid, 1-naphtoic acid,2-naphtoic acid and the like, and hydroxynaphtoic acid is particularlyeffective.

[0199] The above-mentioned aliphatic and aromatic carboxylic acid arepreferably used as a sodium salt, potassium salt or ammonium salt forenhancing water-solubility. The content of an organic carboxylic acid ina developer used in the present invention is not particularlyrestricted, however, when it is less than 0.1% by weight, a sufficienteffect is not obtained, and when 10% by weight or more, a further effectcan not be attained and additionally, dissolving may be prevented whenother additive is used together. Therefore, the addition amount ispreferably 0.1 to 10% by weight, more preferably from 0.5 to 4% byweight based on a developer in use.

[0200] Other Components

[0201] The developer and replenisher used in the present invention canfurther contain a de-foaming agent, water softener and the like, ifnecessary. Examples of the water softener include polyphosphoric acidand sodium, potassium and ammonium salts thereof, aminopolycarboxylicacids such as ethylenediaminetetraacetic acid,diethylenetriaminepentaacetic acid, triethylenetetraminehexaacetic acid,hydroxyethylethylenediaminetriacetic acid, nitrilotriacetic acid,1,2-diaminocyclohexanetetraacetic acid,1,3-diamino-2-propanoltetraacetic acid and the like and sodium,potassium and ammonium salts thereof, aminotri(methylenephosphonicacid), ethylenediaminetetra(methylenephosphonic acid),diethylenetriaminepenta(methylenephosphonic acid),triethylenetetraminehexa(methylenephosphonic acid),hydroxyethylethylenediaminetri (methylenephosphonic acid) and1-hydroxyethane-1,1-diphosphonic acid and sodium, potassium and ammoniumsalts thereof.

[0202] Though the optimum amount of such a water softener used variesdepending on the chelating force thereof, the hardness of hard waterused and the amount of hard water, and general amount used there of isfrom 0.01 to 5% by weight, and more preferably from 0.01 to 0.5% byweight based on a developer used. When the addition amount is below thisrange, the desired object is not attained sufficiently, and when theaddition amount is over this range, reverse effects on image portionssuch as decoloring and the like arise.

[0203] The residual component in the developer and replenisher is water.However, if necessary, various additives known in the art can becontained.

[0204] It is advantageous that the original development replenishing rawsolution and replenisher used in the present invention are prepared asconcentrated solutions containing a smaller amount of water than when inuse, and that they are diluted with water when in use, from thestandpoint of transportation. It is suitable that the degree ofconcentration in this case is such that components do not causeseparation and deposition.

[0205] The temperature of a developer is preferably from 15 to 4° C.,and further preferably from 20 to 35° C. The development time ispreferably from 5 to 60 seconds, and further preferably from 7 to 40seconds.

[0206] A planographic printing plate subjected to development treatmentusing the above-mentioned developer and replenisher is subjected topost-treatment with washing water, a rinse solution containing asurfactant and the like, or a desensitizing solution containing gumArabic and a starch derivative. For post-treatment in the case of useingthe planographic printing plate of the present invention produced by theabove-mentioned method, the above-mentioned treatments can be combinedvariously and used.

[0207] In the method of plate production of the present invention,development is conducted using a developer of which permeability into ahardened recording layer has been regulated as described above.Therefore, parts in the vicinity of the surface having high filmhardness effectively prevent permeation of a developer, and an imagehaving high sensitivity and excellent discrimination can be formedwithout reduction in printing endurance.

[0208] Recently, automatic developing machines for a printing plate arewidely used for rationalization and standardization of plate productionoperation, in plate production and printing industries. A planographicprinting plate obtained according to the present invention can also betreated using this automatic developing machine. This automaticdeveloping machine is, in general, composed of a development section anda post treatment section, and comprises an apparatus for transporting aprinting plate, treating solution vessels, and a spray apparatus, and inwhich developing treatment is conducted by spraying treating solutionssucked up by a pump through spray nozzles while horizontallytransporting a printing plate which has been exposed. Further, recently,there is also known a method in which a printing plate is treated bybeing immersed and transported by a submerged guide roll in a treatingsolution vessel filled with a treatment solution. In such automatictreatment, treatment can also be conducted while replenishing areplenishment solution with a treatment solution in accordance with thetreatment amount, working time and the like. Further, a so-calleddisposable treatment method in which treatment is effected with asubstantially unused treating solution can also be used.

[0209] The planographic printing plate obtained as described above canbe, after application of desensitizing gum if necessary, subjected to aprinting process. For the purpose of improving printing endurance,burning treatment can be performed. When a planographic printing plateis subjected to burning treatment, it is preferable to conduct treatmentwith a surface smoothing solution as described in JP-B Nos. 61-2518 and55-28062, JP-A Nos. 62-31859 and 61-159655, before the burningtreatment. As this method, a method in which the surface smoothingsolution is applied on a planographic printing plate by using sponge orabsorbent cotton soaked with this solution, a method in which a printingplate is immersed in a vat filled with a surface smoothing solution toeffect application on the plate, a method using an automatic coater, andthe like are applied. Further, a more preferable result is obtained if,after application, the applied amount is made uniform by a squeeze orsqueeze roller. The amount of a surface smoothing solution applied is,in general, suitably from 0.03 to 0.8 g/m² (dry weight).

[0210] The planographic printing plate on which a surface smoothingagent has been applied is dried, then, heated to high temperatures by aburning processor (for example, Burning Processor: “BP-1300”, availablefrom Fuji Photo Film Co., Ltd.) and the like. In this case, it ispreferable that the heating temperature is from 180 to 300° C. and theheating time is from 1 to 20 minutes depending on the kinds ofcomponents forming the images.

[0211] The planographic printing plate which has been subjected toburning-treatment can be appropriately subjected, if necessary, toconventionally conducted treatments such as washing with water, gumdrawing and the like, and when smoothing liquid containing awater-soluble polymer compound and the like is used, so-calledde-sensitizing treatments such as gum drawing and the like can beomitted.

[0212] Planographic printing plates obtained by such treatments are putin an offset printing machine and the like, and used in printing of alarge number of sheets.

EXAMPLE

[0213] The following examples illustrates the present invention, but donot limit the scope of the present invention.

Example 1

[0214] Production of Substrate

[0215] An aluminum alloy plate (thickness: 0.30 mm) containing 99.5% ormore of aluminum, 0.30% of Fe, 0.10% of Si, 0.02% of Ti and 0.013% of Cuwas de-greased by washing with trichloroethylene, the surface of whichwas sand-blasted, and washed sufficiently with water.

[0216] This aluminum plate was immersed in a 25% sodium hydroxideaqueous solution (45° C.) for 9 seconds for etching, washed with water,then, further immersed in a 2% HNO₃ aqueous solution for 20 seconds andwashed with water. The amount of etching of the sand-blasted surface atthis point was about 3 g/m².

[0217] Then, a direct current anodized film of 3 g/m² was provided onthe above-mentioned aluminum plate using 7% sulfuric acid as anelectrolyte solution, at a current density of 15 A/dm², and furtherwashed and dried, then, the following application solution for a primerlayer was applied thereon, and dried under an atmosphere of 80° C. for30 seconds. The applied amount after drying was 10 mg/m².

[0218] Preparation of Application Solution for Primer Layer

[0219] An application solution for a primer layer was prepared by mixingcompounds of the following formulation. 2-aminoethylphosphonic acid 0.5g methanol  40 g pure water  60 g

[0220] Synthesis of Polymer

[0221] 2-hydroxyethyl methacrylate, N-(p-sulfamoylphenyl)methacrylamideand methacrylic acid were subjected to radical polymerization by a usualmethod to give a polymer. Further, the obtained polymer was reacted with2-methacryloyloxyethyl isocyanate to obtain a polymer (RB-1) of thefollowing formula. The formulation ratio was 50:30:20=x:y:z. Theweight-average molecular weight was 120000 (based on polystyrene).

[0222] Formation of Recording Layer

[0223] The following recording layer application solution was applied bya wire bar on the above-mentioned substrate carrying thereon a primerlayer formed, and dried at 120° C. for 45 seconds by a hot air modedrying apparatus to form a recording layer, giving a planographicprinting plate of Example 1 [P-1]. The application amount after dryingwas 1.4 g/m².

[0224] The optical density of this recording layer was measured by usinga Hitachi self-recording spectrophotometer (trade name: U-3000,manufactured by Hitachi Ltd.). The measurement was conducted accordingto a reflection method using an integrating sphere, and a substratecarrying neither primer layer nor recording layer applied was used asreference. The maximum absorption wavelength was about 800 nm, and theoptical density was 1.16.

[0225] The structures of an infrared absorbing agent and the like usedin preparation of the recording layer application solution are as shownbelow.

[0226] Recording Layer Application Solution [P-1] Dipentaerythritolhexaacrylate 0.50 g Monomer (TM-1) 0.50 g Polymer (RB-1) 1.00 gNaphthalenesulfonic acid salt of 0.04 g Victoria Pure Bluep-Methoxyphenol 0.001 g  Fluorine-based surfactant 0.03 g (trade name:Megafac F-176, manufactured by Dainippon Ink & Chemicals, Inc.) Methylethyl ketone   10 g γ-Butyrolactone   5 g Methanol   7 g1-methoxy-2-propanol   5 g

[0227]

[0228] Evaluation of Planographic Printing Plate

[0229] 1. Evaluation of Film Hardness

[0230] The planographic printing plate [P-1] was exposed by Trendsetter3244 VFS (tradename) manufactured by Creo, at a plate surface energyamount of 80 mj/cm². After exposure, film hardness was measured by usingan apparatus prepared by mounting a thrusting apparatus (trade name:Triboscope, manufactured by HYSITRON) ontoAFM (interatomicforcemicroscope) SPA300 (trade name) manufactured by Seiko InstrumentsK.K. The film hardness of the upper part of the recording layer was 1.3GPa, the average film hardness was 0.7 GPa, and the ratio of filmhardness was 1.86.

[0231] 2. Evaluation of Permeability

[0232] The planographic printing plate [P-1] was exposed by Trendsetter3244 VFS (tradename) manufactured by Creo, at a plate surface energyamount of 80 mj/cm². After exposure, the plate was immersed into adeveloper [D-1] shown below at 30° C. using 4262A LCR meter (trade name)manufactured by Yokogawa Hewlett Packard K.K., and change inelectrostatic capacity was measured. Change in electrostatic capacityoccurred 70 seconds after immersion. The developer [D-1] had a pH of11.8.

[0233] Developer [D-1] Potassium hydroxide  3 g Potassium hydrogencarbonate  1 g Potassium carbonate  2 g Sodium sulfite  1 g Polyethyleneglycol mononaphthyl ether 150 g Sodium dibutylnaphthalenesulfonate  50 gTetra sodium ethylenediamine tetraacetate  8 g Water 785 g

[0234] 3. Evaluation of Sensitivity

[0235] The planographic printing plate [P-1] was exposed by Trendsetter3244 VFS (tradename) manufactured by Creo, while changing plate surfaceenergy amount by varying output and revolution of an outer drum. Afterexposure, the above-mentioned developer was placed as a chargingsolution into an automatic developing machine (trade name: Stabron 900NP, manufactured by Fuji Photo Film Co., Ltd.), and the plate wastreated by this machine using the following developer [D-2] as areplenisher and further using a 1:1 water diluted solution of FP-2W(trade name, manufactured by Fuji Photo Film Co., Ltd.) as a finisher ata development temperature of 30° C. and a development time of 12seconds. In this procedure, the replenisher was automatically chargedwhile keeping the electric conductivity of the developer in thedeveloping bath of the automatic developing machine constant. Aftertreatment, the plate surface energy at which a clear solid image couldbe formed was 80 mJ/cm². Developer [D-2] Potassium hydroxide 6 gPotassium carbonate 2 g Sodium sulfite 1 g Polyethylene glycolmononaphthyl ether 150 g Sodium dibutylnaphthalenesulfonate 50 gPotassium hydroxyethanediphosphonate 4 g Silicon 0.1 g (trade name:TSA-731, manufactured by Toshiba Silicone K. K.) Water 786.9 g

[0236] 4. Evaluation of Dot Reproducibility

[0237] The planographic printing plate [P-1] was exposed by Trendsetter3244 VFS (tradename)manufactured by Creo, at a plate surface energyamount of 80 mj/cm² and a screen line number of 1751 pi. After exposure,the plate was subjected to development treatment using the samedeveloper and automatic developing machine as in “3. Evaluation ofsensitivity”. The minimum dots and the maximum dots which could bereproduced on the obtained planographic printing plate were observedusing a loupe. 1% of the minimum dots were reproduced and 99% of themaximum dots were reproduced. Both of the minimum dots and the maximumdots were excellent in reproducibility.

[0238] 5. Evaluation of Printing Endurance

[0239] The planographic printing plate [P-1] was exposed by Trendsetter3244 VFS (tradename) manufactured by Creo, at a plate surface energyamount of 80 mj/cm². After exposure, the plate was subjected todevelopment treatment using the same developer and automatic developingmachine as in “3. Evaluation of sensitivity”. The obtained planographicprinting plate was set on a printer (trade name: Risron, manufactured byKomori Corporation), and printing was conducted using commerciallyavailable eco-ink and high quality paper, to obtain 100000 pieces ofprints containing no blank part in image portions and causing nocontamination in non-image portions.

Comparative Example 1

[0240] A planographic printing plate [S-1] of Comparative Example 1 wasobtained in the same manner as in Example 1 except that an applicationsolution for a recording layer [S-1] prepared without using an infraredabsorbing agent (IR-1) was used in the application solution for arecording layer [P-1] used in Example 1.

[0241] The optical density of this recording layer was measured in thesame manner as in Example 1. There was no maximum absorption wavelength,and the optical density at 750 nm to 800 nm was 0.05.

[0242] 1. Evaluation of Film Hardness

[0243] The planographic printing plate [P-1] was exposed by Trendsetter3244 VFS (tradename: manufactured by Creo) at a plate surface energyamount of 80 mj/cm². After exposure, film hardness was measured in thesame manner as in Example 1. The film hardness of the upper part of therecording layer was 0.7 GPa, the average film hardness was 0.7 GPa, andthe ratio of film hardness was 1.0.

[0244] 2. Evaluation of Sensitivity

[0245] The planographic printing plate [P-1] was exposed by Trendsetter3244 VFS (tradename: manufactured by Creo) while changing plate surfaceenergy amount by varying output and revolution of an outer drum. Afterexposure, the above-mentioned developer was placed as a chargingsolution into an automatic developing machine (trade name: Stabron 900NP, manufactured by Fuji Photo Film Co., Ltd.), and the plate wasdeveloped by this machine using the following developer [D-2] as areplenisher and further using a 1:1 water diluted solution of FP-2W(trade name, manufactured by Fuji Photo Film Co., Ltd.) as a finisher.In this procedure, the replenisher was automatically charged whilekeeping the electric conductivity of the developer in the developingbath of the automatic developing machine constant.

[0246] After development, the plate surface energy at which a clearsolid image could be formed was measured. However, image could not beformed even at an energy of 30 mJ/cm².

[0247] Thus, it was found that the planographic printing plate ofComparative Example 1 which has no difference between film hardness inthe upper portion and average film hardness is inferior in sensitivityas compared with this example.

Comparative Example 2

[0248] The planographic printing plate [S-1] produced in ComparativeExample 1 was exposed and evaluated.

[0249] 1. Evaluation of Film Hardness

[0250] The planographic printing plate [S-1] was exposed to ultravioletray by a PS printer having a high pressure mercury lamp mounted. Afterexposure, film hardness was measured in the same manner as inComparative Example 1. The film hardness of the upper portion of therecording layer was 1.1 GPa, the average film hardness was 1.0 GPa, andthe ratio of film hardness was 1.1.

[0251] 2. Evaluation of Dot Reproducibility

[0252] The planographic printing plate [S-1] was exposed to ultravioletrays by a PS printer having a high pressure mercury lamp mounted,through a dot film having a screen line number of 1751 pi. Afterexposure, the plate was subjected to development treatment in the samemanner as in Example 1. The minimum dots and the maximum dots whichcould be reproduced on the obtained planographic printing plate wereobserved using a loupe. Up to 3% of the minimum dots could be reproducedand up to 95% of the maximum dots could be reproduced. It was found thatthe dot reproducibility was poorer than in Example 1 in which an imagewas formed by infrared laser even if the reproducible minimum dot islarger, the reproducible maximum dot is small, and ultraviolet rays ofhigher energy is used for formation of an image.

Example 2

[0253] Production of Substrate

[0254] A molten bath of an aluminum alloy containing 99.5% or more ofaluminum, 0.30% of Fe, 0.10% of Si, 0.02% of Ti and 0.013% of Cu wassubjected to purification treatment and molded. For the purification,de-gassing treatment was effected and ceramic tube filter treatment wasconducted for removing unnecessary gases such as hydrogen and the likein the molded bath. The molding was effected according to a DC moldingmethod. A fragment of 10 mm was cut from the surface of the coagulatedingot having a plate thickness of 500 mm, and subjected tohomogenization treatment at 550° C. for 10 hours so that intermetalliccompounds did not increase in size. Then, the fragment was hot-rolled at400° C. and annealed in a continuous annealing furnace at 500° C. for 60seconds, then, cold-rolled to obtain an aluminum rolled plate having athickness of 0.30 mm. By controlling the roughness of the roll, theaverage surface roughness Ra at the center line after cold-rolling wascontrolled to 0.2 μm. Then, the plate was subjected to a tension levelerfor improvement in flatness.

[0255] Next, surface treatment was conducted for obtaining a substrateof a planographic printing plate.

[0256] First, to remove a rolling oil on the surface of the aluminumplate, the plate was de-greased with a 10% sodium aluminate aqueoussolution at 50° C. for 30 seconds, and neutralized with a 30% sulfuricacid aqueous solution at 50° C. for 30 seconds, and subjected to smutremoval treatment.

[0257] Then, to improve close adherence between a substrate and aphotosensitive layer and to impart water-retaining property to non-imageportions, treatment to roughen the surface of a substrate, namely aso-called sand-blasting treatment was conducted. Electrolyticsand-blasting was effected while keeping the temperature of an aqueoussolution containing 1% of nitric acid and 0.5% of aluminum nitrate at45° C., flowing an aluminum web in the aqueous solution, and applying ananode side electric quantity of 240 C/dm² at alternating wavelength ofduty ratio of 1:1 and a current density of 20 A/dm² by an indirectelectricity feeding cell. Then, the plate was subjected to etchingtreatment at 50° C. for 30 seconds with a 10% sodium aluminate aqueoussolution, and neutralized with a 30% sulfuric acid aqueous solution at50° C. for 30 seconds, and subjected to smut removal treatment.

[0258] For further improving friction resistance, chemical resistanceand water retaining property, an oxide film was formed on a substrate bycarrying out anodizing. A 20% sulfuric acid aqueous solution was used asan electrolyte at 35° C., an anodized film of 2.5 g/M² was formed byconducting electrolysis treatment at a direct current of 14 A/dm² by anindirect electricity feeding cell while transporting an aluminum webthrough the electrolyte.

[0259] Then, for securing hydrophilicity necessary for the printingplate non-image portion, silicate treatment was conducted. In thistreatment, a 1.5% aqueous solution of No. 3 sodium silicate was kept at70° C. and an aluminum web was transported so that the contact time was15 seconds, and water washing was further effected. The amount of Siadhered was 10 mg/m². Ra (surface roughness at center line) of thesubstrate produced as described above was 0.25 μm.

[0260] Priming

[0261] Then, the following primer solution 2 was applied by a wire baron this aluminum substrate, and dried at 90° C. for 30 seconds using ahot air drying apparatus. The coated amount after drying was 10 mg/m².

[0262] Primer Solution 2

[0263] Copolymer of ethyl methacrylate and sodium2-acrylamide-2-methyl-1-propanesulfonate of molar ratio of 0.1 g2-aminoethylphosphonic acid 0.1 g Methanol 50 g Ion exchange water 50 g

[0264] Formation of Recording Layer

[0265] Then, the following recording layer application solution [P-2]was prepared and was applied by a wire bar on the above-mentioned primedaluminum plate, and dried at 115° C. for 45 seconds by a hot air dryingapparatus to form a recording layer. The application amount after dryingwas in a range from 1.2 to 1.3 g/m².

[0266] The optical density of this recording layer was measured in thesame manner as in Example 1. It was found that, the optical density was0.98 at the maximum absorption wavelength of about 810 nm. Recordinglayer application solution [P-2] Infrared absorbing agent (IR-2) 0.08 gOnium salt (KO-3) 0.20 g Trihalomethyl compound (TH-1) 0.10 gDipentaerythritol hexaacrylate 1.00 g Copolymer of allyl methacrylate1.00 g and methacrylic acid (molar ratio 80:20, weight-average molecularweight 140000) Naphthalenesulfonate salt of 0.04 g Victoria Pure BlueHydroquinone 0.001 g Silicon-based surfactant 0.03 g (trade name: TEGOGLIDE100, manufactured by TEGO Chemiservice) Methyl ethyl ketone 10 gMethyl isobutyl ketone 5 g Methanol 7 g 1-methoxy-2-propanol 5 g Water 1g

[0267]

[0268] Formation of Over Coat Layer

[0269] Then, the following application solution for an over coat layerwas prepared, and was applied by a wire bar on the above-mentionedaluminum plate having a recording layer formed, and dried at 100° C. for3 seconds by a hot air drying apparatus to form an over coat layer,giving a negative planographic printing plate [P-2] which is Example2.The application amount after drying was 2.2 g/m². Over coat layerapplication solution Polyvinyl alcohol (degree of saponification 20 g98.5 mol %, degree of polymerization 500) Polyvinylpyrrolidone 2 g(trade name: K30, manufactured by Tokyo Kasei Kogyo K. K., molecularweight = 40000) Nonionic surfactant 0.5 g (trade name; EMALEX NP-10,manufactured by Nippon Emulsion K. K) Distilled water 470 g

[0270] 1. Evaluation of Film Hardness

[0271] The planographic printing plate [P-1] was exposed by Trendsetter3244 VFS (tradename: manufactured by Creo) at a plate surface energyamount of 100 mj/cm². After exposure, the over coat layer was peeled,then, the film hardness was measured in the same manner as in Example 1.The film hardness of the upper part of the recording layer was 1.2 GPa,the average film hardness was 0.6 GPa, and the ratio of film hardnesswas 2.0.

[0272] 2. Evaluation of Dot Reproducibility

[0273] The planographic printing plate [P-2] was exposed by Trendsetter3244 VFS (tradename) manufactured by Creo, at a plate surface energyamount of 100 mj/cm² and a screen line number of 1751 pi. Afterexposure, the above-mentioned developer [D-1] was placed as a chargingsolution into an automatic developing machine (trade name) Stabron 900NP, manufactured by Fuji Photo Film Co., Ltd., and the plate was treatedby this machine using the above-mentioned developer [D-2] as areplenisher and further using a burning developer DC-5 (trade name,manufactured by Fuji Photo Film Co., Ltd.) as a finisher at adevelopment temperature of 30° C. and a development time of 12 seconds.In this procedure, the replenisher was automatically charged whilekeeping the pH of the developer in the developing bath of the automaticdeveloping machine constant. Then, the plate was subjected to burningtreatment at 200° C. for 5 minutes, washed with water, and gum solutionGU-7 (trade name) manufactured by Fuji Photo Film Co., Ltd., was appliedon this. The minimum dots and the maximum dots which could be reproducedon the obtained planographic printing plate were observed using a loupe.1% of the minimum dots were reproduced and 99% of the maximum dots werereproduced. Both of the minimum dots and the maximum dots were excellentin reproducibility.

Reference Example

[0274] 1. Evaluation of Permeability

[0275] The planographic printing plate [P-2] obtained in Example 2 wasexposed by Trendsetter 3244 VFS (tradename, manufactured by Creo, at aplate surface energy amount of 100 mj/cm². After exposure, the plate wasimmersed into a developer [E-1] shown below at 30° C., and change inelectrostatic capacity was measured. Change in electrostatic capacityoccurred 5 seconds after immersion. Developer [E-1] Potassium hydroxide3 g Triethanolamine 50 g Sodium dibutylnaphthalenesulfonate 50 g Tetrasodium ethylenediamine tetraacetate 8 g Water 889 g

[0276] 2. Evaluation of Dot Reproducibility

[0277] The planographic printing plate [S-1] was exposed by Trendsetter3244 VFS (tradename: manufactured by Creo) at a plate surface energyamount of 100 mj/cm² and a screen line number of 1751 pi. Afterexposure, a planographic printing plate was obtained in the same manneras in Example 2 except that Stabron 900 NP (manufactured by Fuji PhotoFilm Co., Ltd.) was used as the automatic developing machine and theabove-mentioned developer [E-1] was used as the charging solution andreplenisher. The minimum dots and the maximum dots which could bereproduced on the obtained planographic printing plate were observedusing a loupe. Up to 4% of the minimum dots could be reproduced and upto 95% of the maximum dots could be reproduced. When development wasthus conducted by using the developer [E-1] having higher permeabilityinto a recording layer, it was found that the reproducible minimum dotis larger and the reproducible maximum dot was smaller, namely, theresults are somewhat inferior, as compared with the evaluation resultsin Example 2 in which the developer [D-1] having suitable permeabilitywas used in development.

[0278] The negative planographic printing plate of the present inventionhas the effects of realizing direct plate production based on digitaldata from a computer and the like using solid laser and semiconductorlaser emitting infrared rays, and has higher sensitivity to theabove-mentioned infrared layer, and in which ablation in a recordinglayer in recording is suppressed, and image forming properties such asdot reproducibility and the like, and printing endurance are excellent.Further, by applying the method of producing a planographic printingplate of the present invention to the above-mentioned negativeplanographic printing plate, a planographic printing plate havingexcellent image forming properties such as dot reproducibility and thelike, and printing endurance can be obtained.

What is claimed is:
 1. A negative planographic printing plate comprising a substrate carrying thereon a recording layer wherein: the recording layer contains a polymerizable compound and an infrared absorbing agent, and a polymerization reaction caused by the action of light or heat decreases solubility of the recording layer in an alkali developer; the optical density of said recording layer is in a range from 0.4 to 2.0; and the film hardness of the upper portion of said recording layer after solubility in an alkali developer is reduced due to the action of light or heat is higher than the average film hardness of the whole recording layer.
 2. A negative planographic printing plate according to claim 1, wherein said recording layer contains an infrared absorbing agent under conditions where ablation does not occur.
 3. A negative planographic printing plate according to claim 1, wherein said recording layer contains (A) an infrared absorbing agent, (B) a radical generator and (C) a radical-polymerizable compound which causes a polymerization reaction with the generated, said polymerization reaction causing hardening.
 4. A negative planographic printing plate according to claim 3, wherein said recording layer further contains (D) a binder polymer.
 5. A negative planographic printing plate according to claim 1, wherein the optical density of said recording layer is in a range from 0.6 to 1.6.
 6. A negative planographic printing plate according to claim 1, wherein the ratio of the film hardness of the upper part of said recording layer to the average film hardness [value of (upper part film hardness/average film hardness)] is 1.2 or more.
 7. A negative planographic printing plate according to claim 3, wherein said infrared absorbing agent (A) is selected from the group consisting of cyanine colorants, squarylium colorants, pyrylium salts, and nickel thiolate complexes.
 8. A negative planographic printing plate according to claim 3, wherein said radical generator (B) is an onium salt.
 9. A method of producing a negative planographic printing plate which comprises a step of exposing a planographic printing plate containing a substrate carrying thereon a recording layer which contains a polymerizable compound and an infrared absorbing agent, and in which a polymerization reaction caused by the action of light or heat decreases solubility of the recording layer in an alkali developer, the optical density of said recording layer is in a range from 0.4 to 2.0, and the film hardness of the upper part of said recording layer after reduction in solubility in an alkali developer due to the action of light or heat is higher than the average film hardness of the recording layer, and a step of developing the plate with a developer, the developer being less capable of permeating through the recording layer after said recording layer is hardend by exposure.
 10. A method of producing a negative planographic printing plate according to claim 9, wherein said recording layer contains an infrared absorbing agent under conditions where ablation does not occur.
 11. A method of producing a negative planographic printing plate according to claim 9, wherein said recording layer contains (A) an infrared absorbing agent, (B) a radical generator and (C) a radical-polymerizable compound which causes a polymerization reaction with the generated radical, said polymerization reaction causing hardening.
 12. A method of producing a negative planographic printing plate according to claim 11, wherein said recording layer further contains (D) a binder polymer.
 13. A method of producing a negative planographic printing plate according to claim 9, wherein the optical density of said recording layer is in a range from 0.6 to 1.6.
 14. A method of producing a negative planographic printing plate according to claim 9, wherein the ratio of the film hardness of the upper part of said recording layer to the average film hardness [value of (upper part film hardness/average film hardness)] is 1.2 or more.
 15. A method of producing a negative planographic printing plate according to claim 11, wherein said infrared absorbing agent (A) is selected from the group consisting of cyanine colorants, squarylium colorants, pyrylium salts, and nickel thiolate complexes.
 16. A method of producing a negative planographic printing plate according to claim 11, wherein said radical generator (B) is an onium salt. 